[C++] is_binary_like_type<T> template condition fails to compile because missing T::is_utf8 member

[kszucs]

Describe the bug, including details regarding any error messages, version, and platform.

Tried to use template condition in the following code snippet:

  std::vector<Chunk> GetChunks(const int16_t* def_levels, const int16_t* rep_levels,
                               int64_t num_levels, const ::arrow::Array& values) {
    auto handle_type = [&](auto&& type) -> std::vector<Chunk> {
      using ArrowType = std::decay_t<decltype(type)>;

      if constexpr (::arrow::is_binary_like_type<ArrowType>::value) {
        return CalculateBinaryLike<::arrow::BinaryArray>(def_levels, rep_levels,
                                                         num_levels, values);
      } else {
        throw ParquetException("Unsupported Arrow array type " +
                               values.type()->ToString());
      }
    };
    return ::arrow::VisitType(*values.type(), handle_type);
  }

but getting compiler error:

/Users/kszucs/Workspace/arrow/cpp/src/arrow/type_traits.h:719:70: error: no member named 'is_utf8' in 'arrow::Time64Type'
  719 |     std::integral_constant<bool, is_base_binary_type<T>::value && T::is_utf8>;
      |                                                                   ~~~^
/Users/kszucs/Workspace/arrow/cpp/src/arrow/type_traits.h:744:36: note: in instantiation of template type alias 'is_string_like_type' requested here
  744 |                                   !is_string_like_type<T>::value) ||
      |                                    ^
/Users/kszucs/Workspace/arrow/cpp/src/parquet/chunker_internal.cc:291:30: note: in instantiation of template type alias 'is_binary_like_type' requested here
  291 |       if constexpr (::arrow::is_binary_like_type<ArrowType>::value) {
      |                              ^
/Users/kszucs/Workspace/arrow/cpp/src/arrow/visit_type_inline.h:84:34: note: in instantiation of function template specialization 'parquet::internal::ContentDefinedChunker::Impl::GetChunks(const int16_t *, const int16_t *, int64_t, const ::arrow::Array &)::(anonymous class)::operator()<const arrow::Time64Type &>' requested here
   84 |     ARROW_GENERATE_FOR_ALL_TYPES(TYPE_VISIT_INLINE);
      |                                  ^
/Users/kszucs/Workspace/arrow/cpp/src/parquet/chunker_internal.cc:299:21: note: in instantiation of function template specialization 'arrow::VisitType<(lambda at /Users/kszucs/Workspace/arrow/cpp/src/parquet/chunker_internal.cc:285:24) &>' requested here
  299 |     return ::arrow::VisitType(*values.type(), handle_type);

Seems like this condition cannot be used on its own without further specifying the type.

Component(s)

C++

[pitrou]

Hmm, that is certainly annoying. @bkietz Could you think of an alternative way of spelling this?

[kszucs]

Also the type_id functions are not always consistently named with the template conditions, see:

/// \brief Check for a binary-like type (i.e. with 32-bit offsets)
///
/// \param[in] type_id the type-id to check
/// \return whether type-id is a binary-like type one
constexpr bool is_binary_like(Type::type type_id) {
  switch (type_id) {
    case Type::BINARY:
    case Type::STRING:
      return true;
    default:
      break;
  }
  return false;
}

and the identically named:

template <typename T>
using is_binary_like_type =
    std::integral_constant<bool, (is_base_binary_type<T>::value &&
                                  !is_string_like_type<T>::value) ||
                                     is_fixed_size_binary_type<T>::value>;