libstdc++: Make copyable-box completely constexpr (LWG 3572)

This LWG issue was approved at the October 2021 plenary and can be
implemented now that std::optional is fully constexpr.

libstdc++-v3/ChangeLog:

	* include/std/ranges (ranges::__detail::__box): Add constexpr to
	assignment operators (LWG 3572).
	* testsuite/std/ranges/adaptors/filter.cc: Check assignment of a
	view that uses copyable-box.
This commit is contained in:
Jonathan Wakely 2022-01-11 14:11:46 +00:00
parent 06bc1b0c53
commit d2dc5305d8
2 changed files with 31 additions and 2 deletions

View File

@ -109,7 +109,8 @@ namespace ranges
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3477. Simplify constraints for semiregular-box
__box&
// 3572. copyable-box should be fully constexpr
constexpr __box&
operator=(const __box& __that)
noexcept(is_nothrow_copy_constructible_v<_Tp>)
requires (!copyable<_Tp>)
@ -124,7 +125,7 @@ namespace ranges
return *this;
}
__box&
constexpr __box&
operator=(__box&& __that)
noexcept(is_nothrow_move_constructible_v<_Tp>)
requires (!movable<_Tp>)

View File

@ -140,6 +140,33 @@ test06()
static_assert(!requires { views::all | filter; });
}
constexpr bool
test07()
{
struct Pred
{
constexpr Pred() { }
constexpr Pred(const Pred&) { }
constexpr Pred(Pred&&) { }
// These make it non-copyable, so non-copyable-box<Pred> will provide
// assignment.
Pred& operator=(const Pred&) = delete;
Pred& operator=(Pred&&) = delete;
bool operator()(int i) const { return i < 10; }
};
int i = 0;
ranges::filter_view v(views::single(i), Pred{});
// LWG 3572. copyable-box should be fully constexpr
v = v;
v = std::move(v);
return true;
}
static_assert( test07() );
int
main()
{
@ -150,4 +177,5 @@ main()
test05<forward_iterator_wrapper>();
test05<random_access_iterator_wrapper>();
test06();
test07();
}