[GitHub] [arrow] c-jamie opened a new pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie opened a new pull request #7635:
URL: https://github.com/apache/arrow/pull/7635


   This PR implements fill null for most primitive types.
   
   Please note this is my first time contribiting to such a project. I've attempted to follow all available guidelines.
   
   There also may be obvious implementation details missing, as I am relatively new to CPP and it's intricacies.


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[GitHub] [arrow] wesm closed pull request #7635: ARROW-1567: [C++] Implement "fill_null" function that replaces null values with a scalar value

[GitBox <gi...@apache.org>]

wesm closed pull request #7635:
URL: https://github.com/apache/arrow/pull/7635


   


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[GitHub] [arrow] wesm commented on pull request #7635: ARROW-1567: [C++] Implement "fill_null" function that replaces null values with a scalar value

[GitBox <gi...@apache.org>]

wesm commented on pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#issuecomment-657136940


   @c-jamie thanks for the patch, could you let me know your ASF JIRA username (or create one if you don't have one) so I can assign the issue to you? 


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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r450986569



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+

Review comment:
       done




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[GitHub] [arrow] wesm commented on pull request #7635: ARROW-1567: [C++] Implement "fill_null" function that replaces null values with a scalar value

[GitBox <gi...@apache.org>]

wesm commented on pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#issuecomment-657133231


   +1, will merge once the build passes


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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r449858843



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  Status Execute() { return VisitTypeInline(*data.type, this); }
+};
+
+void ExecFillNull(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  ScalarFillVisitor dispatch(ctx, *batch[0].array(), out);
+  ctx->SetStatus(dispatch.Execute());
+}
+
+void AddBasicFillNullKernels(ScalarKernel kernel, ScalarFunction* func) {
+  auto AddKernels = [&](const std::vector<std::shared_ptr<DataType>>& types) {
+    for (const std::shared_ptr<DataType>& ty : types) {
+      kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+      DCHECK_OK(func->AddKernel(kernel));
+    }
+  };
+
+  AddKernels(NumericTypes());
+  AddKernels(TemporalTypes());
+
+  std::vector<std::shared_ptr<DataType>> other_types = {boolean()};
+
+  for (auto ty : other_types) {
+    kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+    DCHECK_OK(func->AddKernel(kernel));
+  }
+}
+
+}  // namespace
+
+void RegisterScalarFillNull(FunctionRegistry* registry) {
+  // Fill Null always writes into preallocated memory

Review comment:
       Thanks for taking time to review - please bear with me while I work through all these.
   
   First point makes sense. For the second, do you mind expanding on that for my understanding? Zero copy in relation to what?




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[GitHub] [arrow] wesm commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

wesm commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r449802099



##########
File path: cpp/src/arrow/compute/api_scalar.h
##########
@@ -259,6 +259,27 @@ Result<Datum> IsValid(const Datum& values, ExecContext* ctx = NULLPTR);
 ARROW_EXPORT
 Result<Datum> IsNull(const Datum& values, ExecContext* ctx = NULLPTR);
 
+struct ARROW_EXPORT FillNullOptions : public FunctionOptions {
+  explicit FillNullOptions(Datum fill_value) : fill_value(std::move(fill_value)) {}
+
+  Datum fill_value;
+};

Review comment:
       See comments above. I think this should be implemented as a binary function since the "fill values" could be provided by an array. This also will allow the execution layer to (in the near future) insert implicit casts where needed




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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r450987676



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null_test.cc
##########
@@ -0,0 +1,137 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdio>
+#include <iosfwd>
+#include <locale>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_binary.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api.h"
+#include "arrow/compute/kernels/test_util.h"
+#include "arrow/memory_pool.h"
+#include "arrow/result.h"
+#include "arrow/status.h"
+#include "arrow/testing/gtest_compat.h"
+#include "arrow/testing/gtest_util.h"
+#include "arrow/type.h"
+#include "arrow/type_traits.h"
+
+namespace arrow {
+namespace compute {
+
+template <typename Type, typename T = typename TypeTraits<Type>::c_type>
+void CheckFillNull(const std::shared_ptr<DataType>& type, const std::vector<T>& in_values,
+                   const std::vector<bool>& in_is_valid, const Datum fill_value,
+                   const std::vector<T>& out_values,
+                   const std::vector<bool>& out_is_valid) {
+  std::shared_ptr<Array> input = _MakeArray<Type, T>(type, in_values, in_is_valid);
+  std::shared_ptr<Array> expected = _MakeArray<Type, T>(type, out_values, out_is_valid);
+
+  ASSERT_OK_AND_ASSIGN(Datum datum_out, FillNull(input, fill_value));
+  std::shared_ptr<Array> result = datum_out.make_array();
+  ASSERT_OK(result->ValidateFull());
+  AssertArraysEqual(*expected, *result, /*verbose=*/true);
+}
+
+class TestFillNullKernel : public ::testing::Test {};
+
+template <typename Type>
+class TestFillNullPrimitive : public ::testing::Test {};
+
+typedef ::testing::Types<Int8Type, UInt8Type, Int16Type, UInt16Type, Int32Type,
+                         UInt32Type, Int64Type, UInt64Type, Date32Type, Date64Type>
+    PrimitiveTypes;
+
+TYPED_TEST_SUITE(TestFillNullPrimitive, PrimitiveTypes);
+
+TYPED_TEST(TestFillNullPrimitive, FillNull) {
+  using T = typename TypeParam::c_type;
+  using ScalarType = typename TypeTraits<TypeParam>::ScalarType;
+  auto type = TypeTraits<TypeParam>::type_singleton();
+  auto scalar = std::make_shared<ScalarType>(static_cast<T>(5));
+  // No Nulls
+  CheckFillNull<TypeParam, T>(type, {2, 4, 7, 9}, {true, true, true, true}, Datum(scalar),
+                              {2, 4, 7, 9}, {true, true, true, true});
+  // Some Nulls
+  CheckFillNull<TypeParam, T>(type, {2, 4, 7, 8}, {false, true, false, true},
+                              Datum(scalar), {5, 4, 5, 8}, {true, true, true, true});
+  // Empty Array
+  CheckFillNull<TypeParam, T>(type, {}, {}, Datum(scalar), {}, {});
+}
+
+TEST_F(TestFillNullKernel, FillNullNull) {
+  auto datum = Datum(std::make_shared<NullScalar>());
+  CheckFillNull<NullType, std::nullptr_t>(null(), {0, 0, 0, 0},
+                                          {false, false, false, false}, datum,
+                                          {0, 0, 0, 0}, {false, false, false, false});
+  CheckFillNull<NullType, std::nullptr_t>(null(), {NULL, NULL, NULL, NULL}, {}, datum,
+                                          {NULL, NULL, NULL, NULL}, {});
+  CheckFillNull<NullType, std::nullptr_t>(null(), {0, 0, 0, 0},
+                                          {false, false, false, false}, datum,
+                                          {0, 0, 0, 0}, {false, false, false, false});
+  CheckFillNull<NullType, std::nullptr_t>(null(), {NULL, NULL, NULL, NULL}, {}, datum,
+                                          {NULL, NULL, NULL, NULL}, {});
+}
+
+TEST_F(TestFillNullKernel, FillNullBoolean) {
+  auto scalar1 = std::make_shared<BooleanScalar>(false);
+  auto scalar2 = std::make_shared<BooleanScalar>(true);
+  // no nulls
+  CheckFillNull<BooleanType, bool>(boolean(), {true, false, true, false},
+                                   {true, true, true, true}, Datum(scalar1),
+                                   {true, false, true, false}, {true, true, true, true});
+  // some nulls
+  CheckFillNull<BooleanType, bool>(boolean(), {true, false, true, false},
+                                   {false, true, true, false}, Datum(scalar1),
+                                   {false, false, true, false}, {true, true, true, true});
+  CheckFillNull<BooleanType, bool>(boolean(), {true, false, true, false},
+                                   {false, true, false, false}, Datum(scalar2),
+                                   {true, false, true, true}, {true, true, true, true});
+}
+
+TEST_F(TestFillNullKernel, FillNullTimeStamp) {
+  auto time32_type = time32(TimeUnit::SECOND);
+  auto time64_type = time64(TimeUnit::NANO);
+  auto scalar1 = Datum(std::make_shared<Time32Scalar>(5, time32_type));
+  auto scalar2 = Datum(std::make_shared<Time64Scalar>(6, time64_type));
+  // no nulls
+  CheckFillNull<Time32Type, int32_t>(time32_type, {2, 1, 6, 9}, {true, true, true, true},
+                                     Datum(scalar1), {2, 1, 6, 9},
+                                     {true, true, true, true});
+  CheckFillNull<Time32Type, int32_t>(time32_type, {2, 1, 6, 9},
+                                     {true, false, true, false}, Datum(scalar1),
+                                     {2, 5, 6, 5}, {true, true, true, true});
+  // some nulls
+  CheckFillNull<Time64Type, int64_t>(time64_type, {2, 1, 6, 9}, {true, true, true, true},
+                                     scalar2, {2, 1, 6, 9}, {true, true, true, true});
+  CheckFillNull<Time64Type, int64_t>(time64_type, {2, 1, 6, 9},
+                                     {true, false, true, false}, scalar2, {2, 6, 6, 6},
+                                     {true, true, true, true});
+}
+

Review comment:
       I have included a test case




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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r451159113



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);

Review comment:
       Updated




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[GitHub] [arrow] wesm commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

wesm commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r449802049



##########
File path: cpp/src/arrow/compute/api_scalar.cc
##########
@@ -126,5 +126,24 @@ Result<Datum> Compare(const Datum& left, const Datum& right, CompareOptions opti
 SCALAR_EAGER_UNARY(IsValid, "is_valid")
 SCALAR_EAGER_UNARY(IsNull, "is_null")
 
+Result<Datum> FillNull(const Datum& values, const Datum& fill_value, ExecContext* ctx) {
+  if (!values.is_arraylike()) {
+    return Status::Invalid("Values must be Array or ChunkedArray");
+  }
+
+  if (!fill_value.is_scalar()) {
+    return Status::Invalid("fill value must be a scalar");
+  }
+
+  if (!values.type()->Equals(fill_value.type())) {
+    std::stringstream ss;
+    ss << "Array type didn't match type of fill value: " << values.type()->ToString()
+       << " vs " << fill_value.type()->ToString();
+    return Status::Invalid(ss.str());
+  }

Review comment:
       None of these input validation checks should be here. Instead, the kernel should be implemented as an `Arity::Binary()` kernel with input validation handled by the kernel dispatch / executor layer. It's fine if the initial version has the type signature `Array/Scalar` instead of `Any/Any`

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {

Review comment:
       We'll want to rework this to use BitBlockCounter (see `VisitBitBlocksVoid` in arrow/visitor_inline.h)

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);

Review comment:
       The output is never null (unless the fill value is null), right? So you don't need to touch the validity bitmap. In fact, the default mode of the kernel should not allocate one (also for reasons of zero copy, I will comment below)

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}

Review comment:
       Per above, I think this kernel would be better implemented without a KernelInit function

##########
File path: cpp/src/arrow/compute/api_scalar.h
##########
@@ -259,6 +259,27 @@ Result<Datum> IsValid(const Datum& values, ExecContext* ctx = NULLPTR);
 ARROW_EXPORT
 Result<Datum> IsNull(const Datum& values, ExecContext* ctx = NULLPTR);
 
+struct ARROW_EXPORT FillNullOptions : public FunctionOptions {
+  explicit FillNullOptions(Datum fill_value) : fill_value(std::move(fill_value)) {}
+
+  Datum fill_value;
+};

Review comment:
       See comments above. I think this should be implemented as a binary kernel since the "fill values" could be provided by an array. This also will allow the execution layer to (in the near future) insert implicit casts where needed

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);

Review comment:
       When an array has zero null count, the validity bitmap is immediately discarded, so this action is unneeded

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+

Review comment:
       Remove this line

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {

Review comment:
       We should rework this to use a combination of BitBlockCounter and probably GenerateBitsUnrolled

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  Status Execute() { return VisitTypeInline(*data.type, this); }
+};
+
+void ExecFillNull(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  ScalarFillVisitor dispatch(ctx, *batch[0].array(), out);
+  ctx->SetStatus(dispatch.Execute());
+}
+
+void AddBasicFillNullKernels(ScalarKernel kernel, ScalarFunction* func) {
+  auto AddKernels = [&](const std::vector<std::shared_ptr<DataType>>& types) {
+    for (const std::shared_ptr<DataType>& ty : types) {
+      kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+      DCHECK_OK(func->AddKernel(kernel));
+    }
+  };
+
+  AddKernels(NumericTypes());
+  AddKernels(TemporalTypes());
+
+  std::vector<std::shared_ptr<DataType>> other_types = {boolean()};
+
+  for (auto ty : other_types) {
+    kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+    DCHECK_OK(func->AddKernel(kernel));
+  }
+}
+
+}  // namespace
+
+void RegisterScalarFillNull(FunctionRegistry* registry) {
+  // Fill Null always writes into preallocated memory

Review comment:
       I disagree:
   
   * If the fill value is not null, then the output is non-null, so there is no need to allocate a validity bitmap in most cases. So the default behavior should be to use `NullHandling::COMPUTED_NO_PREALLOCATE` for the nulls
   * Since the kernel can do zero-copy when the input has no nulls, this needs to use `MemAllocation::NO_PREALLOCATE` and instead leave memory allocation to the kernel

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  Status Execute() { return VisitTypeInline(*data.type, this); }

Review comment:
       This will need to be reworked to use the `PhysicalType` attributes so that we don't generate functionally identical binary code e.g. for Int64Type / UInt64Type / TimestampType / Date64Type / DurationType (which all use an 8-byte fixed width C type value)

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null_test.cc
##########
@@ -0,0 +1,137 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdio>
+#include <iosfwd>
+#include <locale>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_binary.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api.h"
+#include "arrow/compute/kernels/test_util.h"
+#include "arrow/memory_pool.h"
+#include "arrow/result.h"
+#include "arrow/status.h"
+#include "arrow/testing/gtest_compat.h"
+#include "arrow/testing/gtest_util.h"
+#include "arrow/type.h"
+#include "arrow/type_traits.h"
+
+namespace arrow {
+namespace compute {
+
+template <typename Type, typename T = typename TypeTraits<Type>::c_type>
+void CheckFillNull(const std::shared_ptr<DataType>& type, const std::vector<T>& in_values,
+                   const std::vector<bool>& in_is_valid, const Datum fill_value,
+                   const std::vector<T>& out_values,
+                   const std::vector<bool>& out_is_valid) {
+  std::shared_ptr<Array> input = _MakeArray<Type, T>(type, in_values, in_is_valid);
+  std::shared_ptr<Array> expected = _MakeArray<Type, T>(type, out_values, out_is_valid);
+
+  ASSERT_OK_AND_ASSIGN(Datum datum_out, FillNull(input, fill_value));
+  std::shared_ptr<Array> result = datum_out.make_array();
+  ASSERT_OK(result->ValidateFull());
+  AssertArraysEqual(*expected, *result, /*verbose=*/true);
+}
+
+class TestFillNullKernel : public ::testing::Test {};
+
+template <typename Type>
+class TestFillNullPrimitive : public ::testing::Test {};
+
+typedef ::testing::Types<Int8Type, UInt8Type, Int16Type, UInt16Type, Int32Type,
+                         UInt32Type, Int64Type, UInt64Type, Date32Type, Date64Type>
+    PrimitiveTypes;

Review comment:
       These are declared elsewhere I think?

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null_test.cc
##########
@@ -0,0 +1,137 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdio>
+#include <iosfwd>
+#include <locale>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_binary.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api.h"
+#include "arrow/compute/kernels/test_util.h"
+#include "arrow/memory_pool.h"
+#include "arrow/result.h"
+#include "arrow/status.h"
+#include "arrow/testing/gtest_compat.h"
+#include "arrow/testing/gtest_util.h"
+#include "arrow/type.h"
+#include "arrow/type_traits.h"
+
+namespace arrow {
+namespace compute {
+
+template <typename Type, typename T = typename TypeTraits<Type>::c_type>
+void CheckFillNull(const std::shared_ptr<DataType>& type, const std::vector<T>& in_values,
+                   const std::vector<bool>& in_is_valid, const Datum fill_value,
+                   const std::vector<T>& out_values,
+                   const std::vector<bool>& out_is_valid) {
+  std::shared_ptr<Array> input = _MakeArray<Type, T>(type, in_values, in_is_valid);
+  std::shared_ptr<Array> expected = _MakeArray<Type, T>(type, out_values, out_is_valid);
+
+  ASSERT_OK_AND_ASSIGN(Datum datum_out, FillNull(input, fill_value));
+  std::shared_ptr<Array> result = datum_out.make_array();
+  ASSERT_OK(result->ValidateFull());
+  AssertArraysEqual(*expected, *result, /*verbose=*/true);
+}

Review comment:
       Can we use the ArrayFromJSON functions instead for specifying the test cases?

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null_test.cc
##########
@@ -0,0 +1,137 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdio>
+#include <iosfwd>
+#include <locale>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_binary.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api.h"
+#include "arrow/compute/kernels/test_util.h"
+#include "arrow/memory_pool.h"
+#include "arrow/result.h"
+#include "arrow/status.h"
+#include "arrow/testing/gtest_compat.h"
+#include "arrow/testing/gtest_util.h"
+#include "arrow/type.h"
+#include "arrow/type_traits.h"
+
+namespace arrow {
+namespace compute {
+
+template <typename Type, typename T = typename TypeTraits<Type>::c_type>
+void CheckFillNull(const std::shared_ptr<DataType>& type, const std::vector<T>& in_values,
+                   const std::vector<bool>& in_is_valid, const Datum fill_value,
+                   const std::vector<T>& out_values,
+                   const std::vector<bool>& out_is_valid) {
+  std::shared_ptr<Array> input = _MakeArray<Type, T>(type, in_values, in_is_valid);
+  std::shared_ptr<Array> expected = _MakeArray<Type, T>(type, out_values, out_is_valid);
+
+  ASSERT_OK_AND_ASSIGN(Datum datum_out, FillNull(input, fill_value));
+  std::shared_ptr<Array> result = datum_out.make_array();
+  ASSERT_OK(result->ValidateFull());
+  AssertArraysEqual(*expected, *result, /*verbose=*/true);
+}
+
+class TestFillNullKernel : public ::testing::Test {};
+
+template <typename Type>
+class TestFillNullPrimitive : public ::testing::Test {};
+
+typedef ::testing::Types<Int8Type, UInt8Type, Int16Type, UInt16Type, Int32Type,
+                         UInt32Type, Int64Type, UInt64Type, Date32Type, Date64Type>
+    PrimitiveTypes;
+
+TYPED_TEST_SUITE(TestFillNullPrimitive, PrimitiveTypes);
+
+TYPED_TEST(TestFillNullPrimitive, FillNull) {
+  using T = typename TypeParam::c_type;
+  using ScalarType = typename TypeTraits<TypeParam>::ScalarType;
+  auto type = TypeTraits<TypeParam>::type_singleton();
+  auto scalar = std::make_shared<ScalarType>(static_cast<T>(5));
+  // No Nulls
+  CheckFillNull<TypeParam, T>(type, {2, 4, 7, 9}, {true, true, true, true}, Datum(scalar),
+                              {2, 4, 7, 9}, {true, true, true, true});
+  // Some Nulls
+  CheckFillNull<TypeParam, T>(type, {2, 4, 7, 8}, {false, true, false, true},
+                              Datum(scalar), {5, 4, 5, 8}, {true, true, true, true});
+  // Empty Array
+  CheckFillNull<TypeParam, T>(type, {}, {}, Datum(scalar), {}, {});
+}
+
+TEST_F(TestFillNullKernel, FillNullNull) {
+  auto datum = Datum(std::make_shared<NullScalar>());
+  CheckFillNull<NullType, std::nullptr_t>(null(), {0, 0, 0, 0},
+                                          {false, false, false, false}, datum,
+                                          {0, 0, 0, 0}, {false, false, false, false});
+  CheckFillNull<NullType, std::nullptr_t>(null(), {NULL, NULL, NULL, NULL}, {}, datum,
+                                          {NULL, NULL, NULL, NULL}, {});
+  CheckFillNull<NullType, std::nullptr_t>(null(), {0, 0, 0, 0},
+                                          {false, false, false, false}, datum,
+                                          {0, 0, 0, 0}, {false, false, false, false});
+  CheckFillNull<NullType, std::nullptr_t>(null(), {NULL, NULL, NULL, NULL}, {}, datum,
+                                          {NULL, NULL, NULL, NULL}, {});
+}
+
+TEST_F(TestFillNullKernel, FillNullBoolean) {
+  auto scalar1 = std::make_shared<BooleanScalar>(false);
+  auto scalar2 = std::make_shared<BooleanScalar>(true);
+  // no nulls
+  CheckFillNull<BooleanType, bool>(boolean(), {true, false, true, false},
+                                   {true, true, true, true}, Datum(scalar1),
+                                   {true, false, true, false}, {true, true, true, true});
+  // some nulls
+  CheckFillNull<BooleanType, bool>(boolean(), {true, false, true, false},
+                                   {false, true, true, false}, Datum(scalar1),
+                                   {false, false, true, false}, {true, true, true, true});
+  CheckFillNull<BooleanType, bool>(boolean(), {true, false, true, false},
+                                   {false, true, false, false}, Datum(scalar2),
+                                   {true, false, true, true}, {true, true, true, true});
+}
+
+TEST_F(TestFillNullKernel, FillNullTimeStamp) {
+  auto time32_type = time32(TimeUnit::SECOND);
+  auto time64_type = time64(TimeUnit::NANO);
+  auto scalar1 = Datum(std::make_shared<Time32Scalar>(5, time32_type));
+  auto scalar2 = Datum(std::make_shared<Time64Scalar>(6, time64_type));
+  // no nulls
+  CheckFillNull<Time32Type, int32_t>(time32_type, {2, 1, 6, 9}, {true, true, true, true},
+                                     Datum(scalar1), {2, 1, 6, 9},
+                                     {true, true, true, true});
+  CheckFillNull<Time32Type, int32_t>(time32_type, {2, 1, 6, 9},
+                                     {true, false, true, false}, Datum(scalar1),
+                                     {2, 5, 6, 5}, {true, true, true, true});
+  // some nulls
+  CheckFillNull<Time64Type, int64_t>(time64_type, {2, 1, 6, 9}, {true, true, true, true},
+                                     scalar2, {2, 1, 6, 9}, {true, true, true, true});
+  CheckFillNull<Time64Type, int64_t>(time64_type, {2, 1, 6, 9},
+                                     {true, false, true, false}, scalar2, {2, 6, 6, 6},
+                                     {true, true, true, true});
+}
+

Review comment:
       The behavior of the kernel when passing a scalar with `is_valid=false` is not validated (and probably yield incorrect results)




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[GitHub] [arrow] c-jamie commented on pull request #7635: ARROW-1567: [C++] Implement "fill_null" function that replaces null values with a scalar value

[GitBox <gi...@apache.org>]

c-jamie commented on pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#issuecomment-657199552


   I've commented on https://issues.apache.org/jira/browse/ARROW-1567
   
   Thanks for all the help!


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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r451159046



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  Status Execute() { return VisitTypeInline(*data.type, this); }

Review comment:
       Updated




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[GitHub] [arrow] wesm commented on pull request #7635: ARROW-1567: [C++] implement fill null

[GitBox <gi...@apache.org>]

wesm commented on pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#issuecomment-657132910


   I changed the implementations to do a single memory allocation and avoid the builder classes, which will be faster, and fixed some other stuff. Additionally, instantiating fewer templates since we can use e.g. a UInt64 template to process all 64-bit types including Double, etc. 


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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r450986751



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);

Review comment:
       I have reworked this.




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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r450989955



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null_test.cc
##########
@@ -0,0 +1,137 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdio>
+#include <iosfwd>
+#include <locale>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_binary.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api.h"
+#include "arrow/compute/kernels/test_util.h"
+#include "arrow/memory_pool.h"
+#include "arrow/result.h"
+#include "arrow/status.h"
+#include "arrow/testing/gtest_compat.h"
+#include "arrow/testing/gtest_util.h"
+#include "arrow/type.h"
+#include "arrow/type_traits.h"
+
+namespace arrow {
+namespace compute {
+
+template <typename Type, typename T = typename TypeTraits<Type>::c_type>
+void CheckFillNull(const std::shared_ptr<DataType>& type, const std::vector<T>& in_values,
+                   const std::vector<bool>& in_is_valid, const Datum fill_value,
+                   const std::vector<T>& out_values,
+                   const std::vector<bool>& out_is_valid) {
+  std::shared_ptr<Array> input = _MakeArray<Type, T>(type, in_values, in_is_valid);
+  std::shared_ptr<Array> expected = _MakeArray<Type, T>(type, out_values, out_is_valid);
+
+  ASSERT_OK_AND_ASSIGN(Datum datum_out, FillNull(input, fill_value));
+  std::shared_ptr<Array> result = datum_out.make_array();
+  ASSERT_OK(result->ValidateFull());
+  AssertArraysEqual(*expected, *result, /*verbose=*/true);
+}
+
+class TestFillNullKernel : public ::testing::Test {};
+
+template <typename Type>
+class TestFillNullPrimitive : public ::testing::Test {};
+
+typedef ::testing::Types<Int8Type, UInt8Type, Int16Type, UInt16Type, Int32Type,
+                         UInt32Type, Int64Type, UInt64Type, Date32Type, Date64Type>
+    PrimitiveTypes;

Review comment:
       I see them declared a couple of times in the code base as PrimitiveDictionaries eg in `scalar_set_lookup_test.cc` - should I use that instead?




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[GitHub] [arrow] wesm commented on a change in pull request #7635: ARROW-1567: [C++] implement fill null

[GitBox <gi...@apache.org>]

wesm commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r453236952



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -32,195 +34,117 @@ namespace internal {
 
 namespace {
 
-template <typename OutType, typename InType, typename Enable = void>
+template <typename Type, typename Enable = void>
 struct FillNullFunctor {};
 
-template <typename OutType, typename InType>
-struct FillNullFunctor<OutType, InType, enable_if_t<is_number_type<InType>::value>> {
-  using value_type = typename TypeTraits<InType>::CType;
-  using BuilderType = typename TypeTraits<OutType>::BuilderType;
+template <typename Type>
+struct FillNullFunctor<Type, enable_if_t<is_number_type<Type>::value>> {
+  using T = typename TypeTraits<Type>::CType;
 
   static void Exec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
-    const Datum& in_arr = batch[0];
-    const Datum& fill_value = batch[1];
-
-    if (!in_arr.is_arraylike()) {
-      ctx->SetStatus(Status::Invalid("Values must be Array or ChunkedArray"));
-    }
-    if (!fill_value.is_scalar()) {
-      ctx->SetStatus(Status::Invalid("fill value must be a scalar"));
-    }

Review comment:
       Note: these type checks are not necessary. You can safely assume that once `Exec` is called that the types have already been checked




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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r450987544



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null_test.cc
##########
@@ -0,0 +1,137 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdio>
+#include <iosfwd>
+#include <locale>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <gtest/gtest.h>
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_binary.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api.h"
+#include "arrow/compute/kernels/test_util.h"
+#include "arrow/memory_pool.h"
+#include "arrow/result.h"
+#include "arrow/status.h"
+#include "arrow/testing/gtest_compat.h"
+#include "arrow/testing/gtest_util.h"
+#include "arrow/type.h"
+#include "arrow/type_traits.h"
+
+namespace arrow {
+namespace compute {
+
+template <typename Type, typename T = typename TypeTraits<Type>::c_type>
+void CheckFillNull(const std::shared_ptr<DataType>& type, const std::vector<T>& in_values,
+                   const std::vector<bool>& in_is_valid, const Datum fill_value,
+                   const std::vector<T>& out_values,
+                   const std::vector<bool>& out_is_valid) {
+  std::shared_ptr<Array> input = _MakeArray<Type, T>(type, in_values, in_is_valid);
+  std::shared_ptr<Array> expected = _MakeArray<Type, T>(type, out_values, out_is_valid);
+
+  ASSERT_OK_AND_ASSIGN(Datum datum_out, FillNull(input, fill_value));
+  std::shared_ptr<Array> result = datum_out.make_array();
+  ASSERT_OK(result->ValidateFull());
+  AssertArraysEqual(*expected, *result, /*verbose=*/true);
+}

Review comment:
       done




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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r450986992



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  Status Execute() { return VisitTypeInline(*data.type, this); }
+};
+
+void ExecFillNull(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  ScalarFillVisitor dispatch(ctx, *batch[0].array(), out);
+  ctx->SetStatus(dispatch.Execute());
+}
+
+void AddBasicFillNullKernels(ScalarKernel kernel, ScalarFunction* func) {
+  auto AddKernels = [&](const std::vector<std::shared_ptr<DataType>>& types) {
+    for (const std::shared_ptr<DataType>& ty : types) {
+      kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+      DCHECK_OK(func->AddKernel(kernel));
+    }
+  };
+
+  AddKernels(NumericTypes());
+  AddKernels(TemporalTypes());
+
+  std::vector<std::shared_ptr<DataType>> other_types = {boolean()};
+
+  for (auto ty : other_types) {
+    kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+    DCHECK_OK(func->AddKernel(kernel));
+  }
+}
+
+}  // namespace
+
+void RegisterScalarFillNull(FunctionRegistry* registry) {
+  // Fill Null always writes into preallocated memory

Review comment:
       Reworked, following your guidance.

##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {

Review comment:
       The has been reworked.




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[GitHub] [arrow] github-actions[bot] commented on pull request #7635: ARROW-1567: [C++] implement fill null

[GitBox <gi...@apache.org>]

github-actions[bot] commented on pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#issuecomment-656606444


   https://issues.apache.org/jira/browse/ARROW-1567


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[GitHub] [arrow] wesm commented on pull request #7635: ARROW-1567: [C++] implement fill null

[GitBox <gi...@apache.org>]

wesm commented on pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#issuecomment-657127070


   This is close to what I'm looking for. I'm going to push some changes to this branch in a little while and then will merge this 


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[GitHub] [arrow] c-jamie commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

c-jamie commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r450986449



##########
File path: cpp/src/arrow/compute/api_scalar.cc
##########
@@ -126,5 +126,24 @@ Result<Datum> Compare(const Datum& left, const Datum& right, CompareOptions opti
 SCALAR_EAGER_UNARY(IsValid, "is_valid")
 SCALAR_EAGER_UNARY(IsNull, "is_null")
 
+Result<Datum> FillNull(const Datum& values, const Datum& fill_value, ExecContext* ctx) {
+  if (!values.is_arraylike()) {
+    return Status::Invalid("Values must be Array or ChunkedArray");
+  }
+
+  if (!fill_value.is_scalar()) {
+    return Status::Invalid("fill value must be a scalar");
+  }
+
+  if (!values.type()->Equals(fill_value.type())) {
+    std::stringstream ss;
+    ss << "Array type didn't match type of fill value: " << values.type()->ToString()
+       << " vs " << fill_value.type()->ToString();
+    return Status::Invalid(ss.str());
+  }

Review comment:
       This has been reworked




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[GitHub] [arrow] github-actions[bot] commented on pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

github-actions[bot] commented on pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#issuecomment-653801598


   https://issues.apache.org/jira/browse/ARROW-1587


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[GitHub] [arrow] wesm commented on a change in pull request #7635: ARROW-1587: [C++] implement fill null

[GitBox <gi...@apache.org>]

wesm commented on a change in pull request #7635:
URL: https://github.com/apache/arrow/pull/7635#discussion_r449877611



##########
File path: cpp/src/arrow/compute/kernels/scalar_fill_null.cc
##########
@@ -0,0 +1,223 @@
+
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "arrow/array/array_base.h"
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/api_scalar.h"
+#include "arrow/compute/kernels/common.h"
+#include "arrow/util/bit_util.h"
+#include "arrow/util/bitmap_writer.h"
+#include "arrow/visitor_inline.h"
+
+namespace arrow {
+
+namespace compute {
+namespace internal {
+namespace {
+
+template <typename T, typename R = void>
+using enable_if_supports_fill_null = enable_if_t<has_c_type<T>::value, R>;
+
+template <typename Type>
+struct FillNullState : public KernelState {
+  explicit FillNullState(MemoryPool* pool) {}
+
+  Status Init(const FillNullOptions& options) {
+    fill_value = options.fill_value.scalar();
+    return Status::OK();
+  }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+template <>
+struct FillNullState<NullType> : public KernelState {
+  explicit FillNullState(MemoryPool*) {}
+
+  Status Init(const FillNullOptions& options) { return Status::OK(); }
+
+  std::shared_ptr<Scalar> fill_value;
+};
+
+struct InitFillNullStateVisitor {
+  KernelContext* ctx;
+  const FillNullOptions* options;
+  std::unique_ptr<KernelState> result;
+
+  InitFillNullStateVisitor(KernelContext* ctx, const FillNullOptions* options)
+      : ctx(ctx), options(options) {}
+
+  template <typename Type>
+  Status Init() {
+    using StateType = FillNullState<Type>;
+    result.reset(new StateType(ctx->exec_context()->memory_pool()));
+    return static_cast<StateType*>(result.get())->Init(*options);
+  }
+
+  Status Visit(const DataType&) { return Init<NullType>(); }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    return Init<Type>();
+  }
+
+  Status GetResult(std::unique_ptr<KernelState>* out) {
+    RETURN_NOT_OK(VisitTypeInline(*options->fill_value.type(), this));
+    *out = std::move(result);
+    return Status::OK();
+  }
+};
+
+std::unique_ptr<KernelState> InitFillNull(KernelContext* ctx,
+                                          const KernelInitArgs& args) {
+  InitFillNullStateVisitor visitor{ctx,
+                                   static_cast<const FillNullOptions*>(args.options)};
+  std::unique_ptr<KernelState> result;
+  ctx->SetStatus(visitor.GetResult(&result));
+  return result;
+}
+
+struct ScalarFillVisitor {
+  KernelContext* ctx;
+  const ArrayData& data;
+  Datum* out;
+
+  ScalarFillVisitor(KernelContext* ctx, const ArrayData& data, Datum* out)
+      : ctx(ctx), data(data), out(out) {}
+
+  Status Visit(const DataType&) {
+    ArrayData* out_arr = out->mutable_array();
+    *out_arr = data;
+    return Status::OK();
+  }
+
+  Status Visit(const BooleanType&) {
+    const auto& state = checked_cast<const FillNullState<BooleanType>&>(*ctx->state());
+    bool value = UnboxScalar<BooleanType>::Unbox(*state.fill_value);
+    ArrayData* out_arr = out->mutable_array();
+    FirstTimeBitmapWriter bit_writer(out_arr->buffers[1]->mutable_data(), out_arr->offset,
+                                     out_arr->length);
+    FirstTimeBitmapWriter bit_writer_validity(out_arr->buffers[0]->mutable_data(),
+                                              out_arr->offset, out_arr->length);
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[1]->data(), data.offset, data.length);
+      BitmapReader bit_reader_validity(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader_validity.IsNotSet()) {
+          if (value == true) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        } else {
+          if (bit_reader.IsSet()) {
+            bit_writer.Set();
+          } else {
+            bit_writer.Clear();
+          }
+          bit_writer_validity.Set();
+        }
+        bit_reader.Next();
+        bit_writer.Next();
+        bit_reader_validity.Next();
+        bit_writer_validity.Next();
+      }
+      bit_writer_validity.Finish();
+      bit_writer.Finish();
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  template <typename Type>
+  enable_if_supports_fill_null<Type, Status> Visit(const Type&) {
+    using T = typename GetViewType<Type>::T;
+    const auto& state = checked_cast<const FillNullState<Type>&>(*ctx->state());
+    T value = UnboxScalar<Type>::Unbox(*state.fill_value);
+    const T* in_data = data.GetValues<T>(1);
+    ArrayData* out_arr = out->mutable_array();
+    auto out_data = out_arr->GetMutableValues<T>(1);
+
+    if (data.null_count != 0) {
+      BitmapReader bit_reader(data.buffers[0]->data(), data.offset, data.length);
+      for (int64_t i = 0; i < data.length; i++) {
+        if (bit_reader.IsNotSet()) {
+          out_data[i] = value;
+        } else {
+          out_data[i] = static_cast<T>(in_data[i]);
+        }
+        bit_reader.Next();
+      }
+      BitUtil::SetBitsTo(out_arr->buffers[0]->mutable_data(), out_arr->offset,
+                         out_arr->length, true);
+    } else {
+      *out_arr = data;
+    }
+    return Status::OK();
+  }
+
+  Status Execute() { return VisitTypeInline(*data.type, this); }
+};
+
+void ExecFillNull(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  ScalarFillVisitor dispatch(ctx, *batch[0].array(), out);
+  ctx->SetStatus(dispatch.Execute());
+}
+
+void AddBasicFillNullKernels(ScalarKernel kernel, ScalarFunction* func) {
+  auto AddKernels = [&](const std::vector<std::shared_ptr<DataType>>& types) {
+    for (const std::shared_ptr<DataType>& ty : types) {
+      kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+      DCHECK_OK(func->AddKernel(kernel));
+    }
+  };
+
+  AddKernels(NumericTypes());
+  AddKernels(TemporalTypes());
+
+  std::vector<std::shared_ptr<DataType>> other_types = {boolean()};
+
+  for (auto ty : other_types) {
+    kernel.signature = KernelSignature::Make({InputType::Array(ty)}, ty);
+    DCHECK_OK(func->AddKernel(kernel));
+  }
+}
+
+}  // namespace
+
+void RegisterScalarFillNull(FunctionRegistry* registry) {
+  // Fill Null always writes into preallocated memory

Review comment:
       You see the places where you're doing
   
   ```
       *out_arr = data;
   ```
   
   I presume your intent is to pass along the memory from the input argument (when the input has no nulls)? That's what's meant by zero-copy, no need to do any processing




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