[libcxx] replaces SFINAE with requires-expressions in bind_front and bind_back
#68249
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cjdb
added
the
libc++
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@llvm/pr-subscribers-libcxx ChangesThe diagnostics for Using requires-expressions gives us a little more context: Full diff: https://github.com/llvm/llvm-project/pull/68249.diff 2 Files Affected:
diff --git a/libcxx/include/__functional/bind_back.h b/libcxx/include/__functional/bind_back.h
index 71dc63c86bdbeed..0dd2befb5240946 100644
--- a/libcxx/include/__functional/bind_back.h
+++ b/libcxx/include/__functional/bind_back.h
@@ -43,14 +43,9 @@ struct __bind_back_t : __perfect_forward<__bind_back_op<tuple_size_v<_BoundArgs>
using __perfect_forward<__bind_back_op<tuple_size_v<_BoundArgs>>, _Fn, _BoundArgs>::__perfect_forward;
};
-template <class _Fn, class ..._Args, class = enable_if_t<
- _And<
- is_constructible<decay_t<_Fn>, _Fn>,
- is_move_constructible<decay_t<_Fn>>,
- is_constructible<decay_t<_Args>, _Args>...,
- is_move_constructible<decay_t<_Args>>...
- >::value
->>
+template <class _Fn, class... _Args>
+ requires is_constructible_v<decay_t<_Fn>, _Fn> && is_move_constructible_v<decay_t<_Fn>> &&
+ (is_constructible_v<decay_t<_Args>, _Args> && ...) && (is_move_constructible_v<decay_t<_Args>> && ...)
_LIBCPP_HIDE_FROM_ABI
constexpr auto __bind_back(_Fn&& __f, _Args&&... __args)
noexcept(noexcept(__bind_back_t<decay_t<_Fn>, tuple<decay_t<_Args>...>>(_VSTD::forward<_Fn>(__f), _VSTD::forward_as_tuple(_VSTD::forward<_Args>(__args)...))))
diff --git a/libcxx/include/__functional/bind_front.h b/libcxx/include/__functional/bind_front.h
index 72bb66480959626..7ccd6e563b6e19e 100644
--- a/libcxx/include/__functional/bind_front.h
+++ b/libcxx/include/__functional/bind_front.h
@@ -42,14 +42,9 @@ struct __bind_front_t : __perfect_forward<__bind_front_op, _Fn, _BoundArgs...> {
using __perfect_forward<__bind_front_op, _Fn, _BoundArgs...>::__perfect_forward;
};
-template <class _Fn, class... _Args, class = enable_if_t<
- _And<
- is_constructible<decay_t<_Fn>, _Fn>,
- is_move_constructible<decay_t<_Fn>>,
- is_constructible<decay_t<_Args>, _Args>...,
- is_move_constructible<decay_t<_Args>>...
- >::value
->>
+template <class _Fn, class... _Args>
+ requires is_constructible_v<decay_t<_Fn>, _Fn> && is_move_constructible_v<decay_t<_Fn>> &&
+ (is_constructible_v<decay_t<_Args>, _Args> && ...) && (is_move_constructible_v<decay_t<_Args>> && ...)
_LIBCPP_HIDE_FROM_ABI
constexpr auto bind_front(_Fn&& __f, _Args&&... __args) {
return __bind_front_t<decay_t<_Fn>, decay_t<_Args>...>(_VSTD::forward<_Fn>(__f), _VSTD::forward<_Args>(__args)...);
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philnik777
approved these changes
Oct 4, 2023
…d `bind_back` The diagnostics for `enable_if_t` are extremely opaque: ``` error: no matching function for call to 'bind_front' note: candidate template ignored: requirement 'integral_constant<bool, false>::value' was not satisfied ``` Using requires-expressions gives us a little more context: ``` error: no matching function for call to 'bind_front' note: candidate template ignored: constraints not satisfied note: because 'is_constructible_v<decay_t<T &>, T &>' evaluated to false ```
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GitHub doesn't have a way to cc folks, so I've added @lnihlen as a reviewer (lemme know if there's a better way to do this). |
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The diagnostics for
enable_if_tare extremely opaque:Using requires-expressions gives us a little more context: