[libc++] Use enable_if_t instead of _EnableIf
I just ran into a compiler error involving __bind_back and some overloads
that were being disabled with _EnableIf. I noticed that the error message
was quite bad and did not mention the reason for the overload being
excluded. Specifically, the error looked like this:
candidate template ignored: substitution failure [with _Args =
<ContiguousView>]: no member named '_EnableIfImpl' in 'std::_MetaBase<false>'
Instead, when using enable_if or enable_if_t, the compiler is clever and
can produce better diagnostics, like so:
candidate template ignored: requirement 'is_invocable_v<
std::__bind_back_op<1, std::integer_sequence<unsigned long, 0>>,
std::ranges::views::__transform::__fn &, std::tuple<PlusOne> &,
ContiguousView>' was not satisfied [with _Args = <ContiguousView>]
Basically, it tries to do a poor man's implementation of concepts, which
is already a lot better than simply complaining about substitution failure.
Hence, this commit uses enable_if_t instead of _EnableIf whenever
possible. That is both more straightforward than using the internal
helper, and also leads to better error messages in those cases.
I understand the motivation for _EnableIf's implementation was to improve
compile-time performance, however I believe striving to improve error
messages is even more important for our QOI, hence this patch. Furthermore,
it is unclear that _EnableIf actually improved compile-time performance
in any noticeable way (see discussion in the review for details).
Differential Revision: https://reviews.llvm.org/D108216
NOKEYCHECK=True
GitOrigin-RevId: 4e0ea2cf2e7c5f04c526f5476eff70280f3c0871
diff --git a/include/array b/include/array
index b76b9fa..0ddfc95 100644
--- a/include/array
+++ b/include/array
@@ -358,7 +358,7 @@
#if _LIBCPP_STD_VER >= 17
template<class _Tp, class... _Args,
- class = _EnableIf<__all<_IsSame<_Tp, _Args>::value...>::value>
+ class = enable_if_t<__all<_IsSame<_Tp, _Args>::value...>::value>
>
array(_Tp, _Args...)
-> array<_Tp, 1 + sizeof...(_Args)>;