bkietz commented on issue #45817:
URL: https://github.com/apache/arrow/issues/45817#issuecomment-2751512786
> Well, I don't know if C++20 concepts could always replace uses of the
`constexpr` functions
`concept`s are directly usable as boolean expressions, for example:
```c++
namespace concepts {
template <typename ArrowType>
concept FixedSizeBinary = std::decay_t<ArrowType>::type_id ==
Type::FIXED_SIZE_BINARY;
}
//...
::arrow::VisitType(*values.type(), [&](const auto& type) {
if constexpr (::arrow::concepts::FixedSizeBinary<decltype(type)>) {
// ...
}
});
```
So I can confidently say we'd lose no expressiveness there. Furthermore, in
the specific case of conditional compilation it's worth noting that `requires`
clauses are also boolean expressions:
```c++
::arrow::VisitType(*values.type(), [&](const auto& type) {
using ArrowType = std::decay_t<decltype(type)>;
constexpr bool HAS_C_TYPE = requires() {
typename ArrowType::c_type;
};
if constexpr (HAS_C_TYPE) {
using c_type = typename ArrowType::c_type;
} else {
// no c_type in ArrowType
}
});
```
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