Re: [PR] feat: implement all functions of bound predicates [iceberg-cpp]

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

shangxinli commented on code in PR #280:
URL: https://github.com/apache/iceberg-cpp/pull/280#discussion_r2484162037


##########
src/iceberg/expression/predicate.cc:
##########
@@ -287,10 +307,10 @@ BoundPredicate::BoundPredicate(Expression::Operation op, std::shared_ptr<BoundTe
 
 BoundPredicate::~BoundPredicate() = default;
 
-Result<Literal::Value> BoundPredicate::Evaluate(const StructLike& data) const {
+Result<Literal> BoundPredicate::Evaluate(const StructLike& data) const {

Review Comment:
   Not sure if we have a tool to capture the API signature changes in release notes. 



##########
src/iceberg/expression/predicate.cc:
##########
@@ -331,12 +376,91 @@ BoundLiteralPredicate::BoundLiteralPredicate(Expression::Operation op,
 
 BoundLiteralPredicate::~BoundLiteralPredicate() = default;
 
-Result<bool> BoundLiteralPredicate::Test(const Literal::Value& value) const {
-  return NotImplemented("BoundLiteralPredicate::Test not implemented");
+Result<bool> BoundLiteralPredicate::Test(const Literal& value) const {

Review Comment:
   Can we add null checking? 
       if (value.IsNull() || literal_.IsNull()) {
         return false;
       }



##########
src/iceberg/expression/literal.cc:
##########
@@ -554,4 +554,51 @@ Result<Literal> LiteralCaster::CastTo(const Literal& literal,
                       target_type->ToString());
 }
 
+// LiteralValueHash implementation
+std::size_t LiteralValueHash::operator()(const Literal::Value& value) const noexcept {
+  return std::visit(
+      [](const auto& v) -> std::size_t {
+        using T = std::decay_t<decltype(v)>;
+
+        constexpr size_t kHashPrime = 0x9e3779b9;
+
+        if constexpr (std::is_same_v<T, std::monostate>) {
+          return 0;
+        } else if constexpr (std::is_same_v<T, Literal::BelowMin>) {
+          return std::numeric_limits<std::size_t>::min();
+        } else if constexpr (std::is_same_v<T, Literal::AboveMax>) {
+          return std::numeric_limits<std::size_t>::max();
+        } else if constexpr (std::is_same_v<T, bool> || std::is_same_v<T, int32_t> ||
+                             std::is_same_v<T, int64_t> || std::is_same_v<T, float> ||
+                             std::is_same_v<T, double> ||
+                             std::is_same_v<T, std::string>) {
+          return std::hash<T>{}(v);
+        } else if constexpr (std::is_same_v<T, std::vector<uint8_t>>) {
+          std::size_t hash = 0;
+          for (size_t i = 0; i < v.size(); ++i) {
+            hash ^= std::hash<uint8_t>{}(v[i]) + kHashPrime + (hash << 6) + (hash >> 2);

Review Comment:
   Hashing identical bytes at different positions can produce same hash (e.g., [1,2] and [2,1] might collide).
   Can we add position i into the hash value to decrease the possibility of collide? 



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