[libcxx-commits] [PATCH] D109212: [libc++] span: replace enable_if with requires. NFCI.

[Arthur O'Dwyer via Phabricator via libcxx-commits]

Quuxplusone added inline comments.


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Comment at: libcxx/include/span:221
 // [span.cons], span constructors, copy, assignment, and destructor
-    template <size_t _Sz = _Extent, enable_if_t<_Sz == 0, nullptr_t> = nullptr>
+    template <size_t _Sz = _Extent> requires(_Sz == 0)
     _LIBCPP_INLINE_VISIBILITY constexpr span() noexcept : __data{nullptr} {}
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> `enable_if_t` which is verbose and slow

I benchmarked `enable_if_t` versus `_EnableIf` versus `requires` over at https://reviews.llvm.org/D108216#inline-1037983 a couple days ago, and it seemed that `requires` was about 20% slower than `enable_if_t`/`_EnableIf`. What evidence led you to the "and slow" part of your comment?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109212/new/

https://reviews.llvm.org/D109212