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 <jwak...@redhat.com>
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>
