On 05/11/20 19:09 +0000, Jonathan Wakely wrote:
The relational operators for std::optional were using the wrong types in the declval expressions used to constrain them. Instead of using const lvalues they were using non-const rvalues, which meant that a type might satisfy the constraints but then give an error when the function body was instantiated.libstdc++-v3/ChangeLog: PR libstdc++/96269 * include/std/optional (operator==, operator!=, operator<) (operator>, operator<=, operator>=): Fix types used in SFINAE constraints. * testsuite/20_util/optional/relops/96269.cc: New test. Tested powerpc64le-linux. Committed to trunk.
When concepts are supported we can make the alias templates __optional_eq_t et al use a requires-expression instead of SFINAE. This is potentially faster to compile, given expected improvements to C++20 compilers. I'm testing this patch.
commit c5d8e2ba0ad20425cc7778152824d9e5267b0ec5 Author: Jonathan Wakely <[email protected]> Date: Thu Nov 5 19:45:52 2020 libstdc++: Use concepts to constrain std::optional relops When concepts are supported we can make the alias templates __optional_eq_t et al use a requires-expression instead of SFINAE. This is potentially faster to compile, given expected improvements to C++20 compilers. libstdc++-v3/ChangeLog: * include/std/optional [__cpp_concepts] (__optional_eq_t) (__optional_ne_t, __optional_lt_t, __optional_gt_t) (__optional_le_t, __optional_ge_t): Use requires-clause on alias template. diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional index 5ea5b39d0e69..4e9618648250 100644 --- a/libstdc++-v3/include/std/optional +++ b/libstdc++-v3/include/std/optional @@ -998,9 +998,48 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION void reset() noexcept { this->_M_reset(); } }; +#if __cpp_lib_concepts + template<typename _Tp, typename _Up> + requires requires (const _Tp __t, const _Up __u) { + { __t == __u } -> convertible_to<bool>; + } + using __optional_eq_t = bool; + + template<typename _Tp, typename _Up> + requires requires (const _Tp __t, const _Up __u) { + { __t != __u } -> convertible_to<bool>; + } + using __optional_ne_t = bool; + + template<typename _Tp, typename _Up> + requires requires (const _Tp __t, const _Up __u) { + { __t < __u } -> convertible_to<bool>; + } + using __optional_lt_t = bool; + + template<typename _Tp, typename _Up> + requires requires (const _Tp __t, const _Up __u) { + { __t > __u } -> convertible_to<bool>; + } + using __optional_gt_t = bool; + + template<typename _Tp, typename _Up> + requires requires (const _Tp __t, const _Up __u) { + { __t <= __u } -> convertible_to<bool>; + } + using __optional_le_t = bool; + + template<typename _Tp, typename _Up> + requires requires (const _Tp __t, const _Up __u) { + { __t >= __u } -> convertible_to<bool>; + } + using __optional_ge_t = bool; + +#else // concepts + template<typename _Tp> using __optional_relop_t = - enable_if_t<is_convertible<_Tp, bool>::value, bool>; + enable_if_t<is_convertible_v<_Tp, bool>, bool>; template<typename _Tp, typename _Up> using __optional_eq_t = __optional_relop_t< @@ -1031,6 +1070,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION using __optional_ge_t = __optional_relop_t< decltype(std::declval<const _Tp&>() >= std::declval<const _Up&>()) >; +#endif // concepts // Comparisons between optional values. template<typename _Tp, typename _Up>
