On Wed, 8 Mar 2023 at 14:36, Patrick Palka via Libstdc++
<libstd...@gcc.gnu.org> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk and perhaps 12?
Yes, OK for trunk and 12.
>
> PR libstdc++/108362
>
> libstdc++-v3/ChangeLog:
>
> * include/std/ranges (__detail::__can_single_view): New concept.
> (_Single::operator()): Constrain it. Move [[nodiscard]] to the
> end of the function declarator.
> (__detail::__can_iota_view): New concept.
> (_Iota::operator()): Constrain it. Move [[nodiscard]] to the
> end of the function declarator.
> (__detail::__can_istream_view): New concept.
> (_Istream::operator()): Constrain it. Move [[nodiscard]] to the
> end of the function declarator.
> * testsuite/std/ranges/iota/iota_view.cc (test07): New test.
> * testsuite/std/ranges/istream_view.cc (test08): New test.
> * testsuite/std/ranges/single_view.cc (test07): New test.
> ---
> libstdc++-v3/include/std/ranges | 40 ++++++++++++++-----
> .../testsuite/std/ranges/iota/iota_view.cc | 10 +++++
> .../testsuite/std/ranges/istream_view.cc | 12 ++++++
> .../testsuite/std/ranges/single_view.cc | 13 ++++++
> 4 files changed, 65 insertions(+), 10 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index 0a65d74bb5b..67566c6ebcf 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -675,30 +675,41 @@ namespace views
> template<typename _Tp>
> inline constexpr empty_view<_Tp> empty{};
>
> + namespace __detail
> + {
> + template<typename _Tp>
> + concept __can_single_view
> + = requires { single_view<decay_t<_Tp>>(std::declval<_Tp>()); };
> + } // namespace __detail
> +
> struct _Single
> {
> - template<typename _Tp>
> - [[nodiscard]]
> + template<__detail::__can_single_view _Tp>
> constexpr auto
> - operator()(_Tp&& __e) const
> + operator() [[nodiscard]] (_Tp&& __e) const
> noexcept(noexcept(single_view<decay_t<_Tp>>(std::forward<_Tp>(__e))))
> { return single_view<decay_t<_Tp>>(std::forward<_Tp>(__e)); }
> };
>
> inline constexpr _Single single{};
>
> + namespace __detail
> + {
> + template<typename... _Args>
> + concept __can_iota_view = requires {
> iota_view(std::declval<_Args>()...); };
> + } // namespace __detail
> +
> struct _Iota
> {
> - template<typename _Tp>
> - [[nodiscard]]
> + template<__detail::__can_iota_view _Tp>
> constexpr auto
> - operator()(_Tp&& __e) const
> + operator() [[nodiscard]] (_Tp&& __e) const
> { return iota_view(std::forward<_Tp>(__e)); }
>
> template<typename _Tp, typename _Up>
> - [[nodiscard]]
> + requires __detail::__can_iota_view<_Tp, _Up>
> constexpr auto
> - operator()(_Tp&& __e, _Up&& __f) const
> + operator() [[nodiscard]] (_Tp&& __e, _Up&& __f) const
> { return iota_view(std::forward<_Tp>(__e), std::forward<_Up>(__f)); }
> };
>
> @@ -796,13 +807,22 @@ namespace views
>
> namespace views
> {
> + namespace __detail
> + {
> + template<typename _Tp, typename _Up>
> + concept __can_istream_view
> + = requires (_Up __e) {
> + basic_istream_view<_Tp, typename _Up::char_type, typename
> _Up::traits_type>(__e);
> + };
> + };
> +
> template<typename _Tp>
> struct _Istream
> {
> template<typename _CharT, typename _Traits>
> - [[nodiscard]]
> constexpr auto
> - operator()(basic_istream<_CharT, _Traits>& __e) const
> + operator() [[nodiscard]] (basic_istream<_CharT, _Traits>& __e) const
> + requires __detail::__can_istream_view<_Tp,
> std::remove_reference_t<decltype(__e)>>
> { return basic_istream_view<_Tp, _CharT, _Traits>(__e); }
> };
>
> diff --git a/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> b/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> index 2dd17113536..0d2eaf1d0c2 100644
> --- a/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/iota/iota_view.cc
> @@ -110,6 +110,15 @@ test06()
> VERIFY( std::ranges::equal(v3, w3) );
> }
>
> +template<auto iota = std::views::iota>
> +void
> +test07()
> +{
> + // Verify SFINAE behavior.
> + static_assert(!requires { iota(nullptr); });
> + static_assert(!requires { iota(nullptr, nullptr); });
> +}
> +
> int
> main()
> {
> @@ -119,4 +128,5 @@ main()
> test04();
> test05();
> test06();
> + test07();
> }
> diff --git a/libstdc++-v3/testsuite/std/ranges/istream_view.cc
> b/libstdc++-v3/testsuite/std/ranges/istream_view.cc
> index 26f109fdeaa..cc1c3e006b9 100644
> --- a/libstdc++-v3/testsuite/std/ranges/istream_view.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/istream_view.cc
> @@ -115,6 +115,17 @@ test07()
> VERIFY( sum == 10 );
> }
>
> +template<class T, class U>
> +concept can_istream_view = requires (U u) { views::istream<T>(u); };
> +
> +void
> +test08()
> +{
> + // Verify SFINAE behavior.
> + struct S { };
> + static_assert(!can_istream_view<S, std::istringstream>);
> +}
> +
> int
> main()
> {
> @@ -125,4 +136,5 @@ main()
> test05();
> test06();
> test07();
> + test08();
> }
> diff --git a/libstdc++-v3/testsuite/std/ranges/single_view.cc
> b/libstdc++-v3/testsuite/std/ranges/single_view.cc
> index 063caeb8785..38a3946ca43 100644
> --- a/libstdc++-v3/testsuite/std/ranges/single_view.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/single_view.cc
> @@ -111,6 +111,18 @@ test06()
> auto y = std::views::single(std::move(obj));
> }
>
> +template<auto single = std::views::single>
> +void
> +test07()
> +{
> + // Verify SFINAE behavior.
> + struct uncopyable {
> + uncopyable();
> + uncopyable(const uncopyable&) = delete;
> + };
> + static_assert(!requires { single(uncopyable{}); });
> +}
> +
> int main()
> {
> test01();
> @@ -119,4 +131,5 @@ int main()
> test04();
> test05();
> test06();
> + test07();
> }
> --
> 2.40.0.rc0.57.g454dfcbddf
>
