bkietz commented on issue #45817:
URL: https://github.com/apache/arrow/issues/45817#issuecomment-2749346599
I've proposed it elsewhere, but a potentially much nicer way to handle type
visitation is:
```c++
std::vector<Chunk> GetChunks(const int16_t* def_levels, const int16_t*
rep_levels,
int64_t num_levels, const ::arrow::Array&
values) {
return VisitTraits(*values.type(), [&](auto t) {
if constexpr (t.is_binary && !t.is_utf8) {
return CalculateBinaryLike<::arrow::BinaryArray>(def_levels,
rep_levels,
num_levels, values);
}
throw ParquetException("Unsupported Arrow array type " +
values.type()->ToString());
});
}
```
Which could be implemented like:
```c++
template <typename Visitor>
auto VisitTraits(const DataType& type, Visitor trait_visitor) {
return VisitType(type, [&](const auto& type) {
using T = std::decay_t<decltype(type)>;
struct Traits {
static constexpr Type::type id = T::type_id;
enum : bool {
is_fixed_size_binary = id == Type::FIXED_SIZE_BINARY,
is_utf8 = id == Type::STRING || id == Type::LARGE_STRING || id ==
Type::STRING_VIEW,
/// for this visitor, we consider something binary if its array
slots are byte spans
is_binary = (
id == Type::BINARY|| id == Type::LARGE_BINARY || id ==
Type::BINARY_VIEW
|| is_utf8 || is_fixed_size_binary
),
// ...
};
static constexpr int bit_width = ::arrow::bit_width(id);
using OffsetType = OffsetTypeOrVoid<T>;
using CType = CTypeOrVoid<T>;
// ...
};
return trait_visitor(Traits{});
});
}
```
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