Thanks for the review! But I don't have a commit access, could you help me
to commit this patch? Many thanks!
> Perhaps we want to backport this, not sure how far back
Is there anything I need to do about this?
Best regards,
Yihan
Patrick Palka <ppa...@redhat.com> 于2025年8月19日周二 23:16写道：
> LGTM! Perhaps we want to backport this, not sure how far back
> (std::expected was implemented in GCC 12).
>
> On Sat, 16 Aug 2025, Yihan Wang wrote:
>
> > libstdc++-v3/ChangeLog:
> >
> > * include/std/expected: Add missing constraint as per LWG 4222.
> > * testsuite/20_util/expected/lwg4222.cc: New test.
> >
> > Signed-off-by: Yihan Wang <yronglin...@gmail.com>
> > ---
> > libstdc++-v3/include/std/expected | 1 +
> > .../testsuite/20_util/expected/lwg4222.cc | 39 +++++++++++++++++++
> > 2 files changed, 40 insertions(+)
> > create mode 100644 libstdc++-v3/testsuite/20_util/expected/lwg4222.cc
> >
> > diff --git a/libstdc++-v3/include/std/expected
> b/libstdc++-v3/include/std/expected
> > index 60f1565f15b..4eaaab693e1 100644
> > --- a/libstdc++-v3/include/std/expected
> > +++ b/libstdc++-v3/include/std/expected
> > @@ -474,6 +474,7 @@ namespace __expected
> > template<typename _Up = remove_cv_t<_Tp>>
> > requires (!is_same_v<remove_cvref_t<_Up>, expected>)
> > && (!is_same_v<remove_cvref_t<_Up>, in_place_t>)
> > + && (!is_same_v<remove_cvref_t<_Up>, unexpect_t>)
> > && is_constructible_v<_Tp, _Up>
> > && (!__expected::__is_unexpected<remove_cvref_t<_Up>>)
> > && __expected::__not_constructing_bool_from_expected<_Tp, _Up>
> > diff --git a/libstdc++-v3/testsuite/20_util/expected/lwg4222.cc
> b/libstdc++-v3/testsuite/20_util/expected/lwg4222.cc
> > new file mode 100644
> > index 00000000000..5c107792456
> > --- /dev/null
> > +++ b/libstdc++-v3/testsuite/20_util/expected/lwg4222.cc
> > @@ -0,0 +1,39 @@
> > +// { dg-do run { target c++23 } }
> > +
> > +// LWG 4222. 'expected' constructor from a single value missing a
> constraint
> > +
> > +#include <expected>
> > +#include <type_traits>
> > +#include <testsuite_hooks.h>
> > +
> > +struct T {
> > + explicit T(auto) {}
> > +};
> > +struct E {
> > + E(int) {}
> > +};
> > +
> > +struct V {
> > + explicit constexpr V(std::unexpect_t) {}
> > +};
> > +
> > +static_assert(!std::is_constructible_v<std::expected<T, E>,
> std::unexpect_t>);
> > +static_assert(!std::is_constructible_v<std::expected<T, E>,
> std::unexpect_t &>);
> > +static_assert(!std::is_constructible_v<std::expected<T, E>,
> std::unexpect_t &&>);
> > +static_assert(!std::is_constructible_v<std::expected<T, E>, const
> std::unexpect_t>);
> > +static_assert(!std::is_constructible_v<std::expected<T, E>, const
> std::unexpect_t &>);
> > +static_assert(!std::is_constructible_v<std::expected<T, E>, const
> std::unexpect_t &&>);
> > +
> > +constexpr bool test() {
> > + std::expected<V, int> e1(std::in_place, std::unexpect);
> > + VERIFY( e1.has_value() );
> > + std::expected<int, V> e2(std::unexpect, std::unexpect);
> > + VERIFY( !e2.has_value() );
> > + return true;
> > +}
> > +
> > +int main() {
> > + test();
> > + static_assert(test());
> > + return 0;
> > +}
> > --
> > 2.39.5
> >
> >
>
>
