[GitHub] [arrow] pitrou commented on a diff in pull request #35522: GH-35521: [C++] Hash null bitmap only if null count is 0

["pitrou (via GitHub)" <gi...@apache.org>]

pitrou commented on code in PR #35522:
URL: https://github.com/apache/arrow/pull/35522#discussion_r1189815220


##########
cpp/src/arrow/scalar_test.cc:
##########
@@ -1106,6 +1106,25 @@ class TestListScalar : public ::testing::Test {
     ASSERT_RAISES(Invalid, scalar.ValidateFull());
   }
 
+  void TestHashing() {
+    ScalarType empty_bitmap_scalar(ArrayFromJSON(int16(), "[1, 2, 3]"));
+    ASSERT_OK(empty_bitmap_scalar.ValidateFull());
+    ASSERT_TRUE(empty_bitmap_scalar.value->data()->buffers[0] == nullptr);
+    
+    auto data = empty_bitmap_scalar.value->data()->buffers[1];
+    std::vector<uint8_t> bitmap_data = {0,0,0};
+    auto null_bitmap = std::make_shared<Buffer>(bitmap_data.data(), 3);
+
+    std::shared_ptr<Int16Array> arr(new Int16Array(3, data, null_bitmap, 0));
+    ASSERT_TRUE(arr->null_count() == 0);
+    // this line fails - I don't know how to create an array with a null bitmap
+    // that is all 0s.
+    ASSERT_TRUE(arr->data()->buffers[0] != nullptr);
+    ScalarType set_bitmap_scalar(arr);

Review Comment:
   Yes, just rewrite the Python snippet (or some equivalent) in C++.  It should actually be easy, using `ArrayFromJSON` and `Array::GetScalar`.



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