Allow optional to tolerate being used with a nested class.
When Clang tries to complete a type containing `std::optional` it
considers the `in_place_t` constructor with no arguments which checks
if the value type is default constructible. If the value type is a
nested class type, then this check occurs too early and poisons the
is_default_constructible trait.
This patch makes optional deduce `in_place_t` so we can prevent
this early SFINAE evaluation. Technically this could break people
doing weird things with the in_place_t tag, but that seems less
important than making the nested class case work.
llvm-svn: 355877
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 86af6f5088b16c98e7033a6a5cf3c889c5d95e57
diff --git a/include/optional b/include/optional
index be584b3..7c136ae 100644
--- a/include/optional
+++ b/include/optional
@@ -687,11 +687,15 @@
_LIBCPP_INLINE_VISIBILITY constexpr optional(optional&&) = default;
_LIBCPP_INLINE_VISIBILITY constexpr optional(nullopt_t) noexcept {}
- template <class... _Args, class = enable_if_t<
- is_constructible_v<value_type, _Args...>>
+ template <class _InPlaceT, class... _Args, class = enable_if_t<
+ __lazy_and<
+ is_same<_InPlaceT, in_place_t>,
+ is_constructible<value_type, _Args...>
+ >::value
+ >
>
_LIBCPP_INLINE_VISIBILITY
- constexpr explicit optional(in_place_t, _Args&&... __args)
+ constexpr explicit optional(_InPlaceT, _Args&&... __args)
: __base(in_place, _VSTD::forward<_Args>(__args)...) {}
template <class _Up, class... _Args, class = enable_if_t<