libstdc++: Invert relationship between std::is_clock and std::is_clock_v
This redefines std::is_clock in terms of std::is_clock_v, instead of the other way around. This avoids instantiatng the class template for code that only uses the variable template. libstdc++-v3/ChangeLog: * include/bits/chrono.h (is_clock_v): Define to false. (is_clock_v<T>): Define partial specialization for true cases. (is_clock): Define in terms of is_clock_v.
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@ -273,16 +273,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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#endif // C++17
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#if __cplusplus > 201703L
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template<typename _Tp>
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struct is_clock;
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template<typename _Tp>
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inline constexpr bool is_clock_v = is_clock<_Tp>::value;
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#if __cpp_lib_concepts
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template<typename _Tp>
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struct is_clock : false_type
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{ };
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inline constexpr bool is_clock_v = false;
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template<typename _Tp>
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requires requires {
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@ -298,32 +291,30 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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requires same_as<typename _Tp::time_point::duration,
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typename _Tp::duration>;
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}
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struct is_clock<_Tp> : true_type
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{ };
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inline constexpr bool is_clock_v<_Tp> = true;
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#else
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template<typename _Tp, typename = void>
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struct __is_clock_impl : false_type
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{ };
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inline constexpr bool is_clock_v = false;
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template<typename _Tp>
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struct __is_clock_impl<_Tp,
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void_t<typename _Tp::rep, typename _Tp::period,
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typename _Tp::duration,
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typename _Tp::time_point::duration,
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decltype(_Tp::is_steady),
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decltype(_Tp::now())>>
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: __and_<is_same<typename _Tp::duration,
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duration<typename _Tp::rep, typename _Tp::period>>,
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is_same<typename _Tp::time_point::duration,
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typename _Tp::duration>,
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is_same<decltype(&_Tp::is_steady), const bool*>,
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is_same<decltype(_Tp::now()), typename _Tp::time_point>>::type
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{ };
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template<typename _Tp>
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struct is_clock : __is_clock_impl<_Tp>::type
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{ };
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inline constexpr bool
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is_clock_v<_Tp, void_t<typename _Tp::rep, typename _Tp::period,
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typename _Tp::duration,
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typename _Tp::time_point::duration,
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decltype(_Tp::is_steady),
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decltype(_Tp::now())>>
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= __and_v<is_same<typename _Tp::duration,
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duration<typename _Tp::rep, typename _Tp::period>>,
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is_same<typename _Tp::time_point::duration,
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typename _Tp::duration>,
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is_same<decltype(&_Tp::is_steady), const bool*>,
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is_same<decltype(_Tp::now()), typename _Tp::time_point>>;
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#endif
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template<typename _Tp>
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struct is_clock
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: bool_constant<is_clock_v<_Tp>>
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{ };
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#endif // C++20
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#if __cplusplus >= 201703L
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