libstdc++: Make std::chrono::duration use reduced ratio for period
This implements the changes from P0548 "common_type and duration". That was a change for C++17, but as it corrects some issues introduced by DRs I'm also treating it as a DR and changing it for all modes from C++11 up. The main change is that duration<R,P>::period no longer denotes P, but rather P::type, the reduced ratio. The unary operator+ and operator- members of duration should now return a duration using that reduced ratio. The requirement that common_type<T>::type is the same type as common_type<T, T>::type (rather than simply T) was already implemented for PR 89102. The standard says that duration::operator+() and duration::operator-() should return common_type_t<duration>, but that seems unnecessarily expensive to compute. This change just uses duration<rep, period> which is the same type, so we don't need to instantiate common_type. As an optimization, this also adds partial specializations of common_type for two durations of the same type, a single duration, two time_points of the same type, and a single time_point. These specializations avoid instantiating other specializations of common_type and one or both of __duration_common_type or __timepoint_common_type for the cases where the answer is trivial to obtain. libstdc++-v3/ChangeLog: * include/std/chrono (__duration_common_type): Ensure the reduced ratio is used. Remove unused partial specialization using __failure_type. (common_type): Pass reduced ratios to __duration_common_type. Add partial specializations for simple cases involving a single duration or time_point type. (duration::period): Use reduced ratio. (duration::operator+(), duration::operator-()): Return duration type using the reduced ratio. * testsuite/20_util/duration/requirements/typedefs_neg2.cc: Adjust expected errors. * testsuite/20_util/duration/requirements/reduced_period.cc: New test.
This commit is contained in:
Jonathan Wakely
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33a55fdb1e
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82030d5101
@ -94,13 +94,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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(_Period1::den / __gcd_den::value) * _Period2::den>;
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public:
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using type = chrono::duration<__cr, __r>;
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using type = chrono::duration<__cr, typename __r::type>;
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};
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template<typename _Period1, typename _Period2>
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struct __duration_common_type<__failure_type, _Period1, _Period2>
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{ typedef __failure_type type; };
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/// @endcond
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/// Specialization of common_type for chrono::duration types.
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@ -108,9 +104,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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template<typename _Rep1, typename _Period1, typename _Rep2, typename _Period2>
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struct common_type<chrono::duration<_Rep1, _Period1>,
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chrono::duration<_Rep2, _Period2>>
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: __duration_common_type<common_type<_Rep1, _Rep2>, _Period1, _Period2>
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: __duration_common_type<common_type<_Rep1, _Rep2>,
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typename _Period1::type,
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typename _Period2::type>
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{ };
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/// Specialization of common_type for two identical chrono::duration types.
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/// @relates duration
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template<typename _Rep, typename _Period>
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struct common_type<chrono::duration<_Rep, _Period>,
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chrono::duration<_Rep, _Period>>
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{ using type = chrono::duration<_Rep, typename _Period::type>; };
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/// Specialization of common_type for one chrono::duration type.
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/// @relates duration
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template<typename _Rep, typename _Period>
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struct common_type<chrono::duration<_Rep, _Period>>
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{ using type = chrono::duration<_Rep, typename _Period::type>; };
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// 20.11.4.3 specialization of common_type (for time_point, sfinae-friendly)
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/// @cond undocumented
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@ -135,6 +146,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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: __timepoint_common_type<common_type<_Duration1, _Duration2>, _Clock>
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{ };
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/// Specialization of common_type for two identical chrono::time_point types.
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/// @relates time_point
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template<typename _Clock, typename _Duration>
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struct common_type<chrono::time_point<_Clock, _Duration>,
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chrono::time_point<_Clock, _Duration>>
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{ using type = chrono::time_point<_Clock, _Duration>; };
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/// Specialization of common_type for one chrono::time_point type.
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/// @relates time_point
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template<typename _Clock, typename _Duration>
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struct common_type<chrono::time_point<_Clock, _Duration>>
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{ using type = chrono::time_point<_Clock, _Duration>; };
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// @} group chrono
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namespace chrono
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@ -401,8 +425,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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public:
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typedef _Rep rep;
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typedef _Period period;
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using rep = _Rep;
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using period = typename _Period::type;
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static_assert(!__is_duration<_Rep>::value, "rep cannot be a duration");
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static_assert(__is_ratio<_Period>::value,
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@ -438,11 +462,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
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{ return __r; }
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// 20.11.5.3 arithmetic
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constexpr duration
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constexpr duration<rep, period>
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operator+() const
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{ return *this; }
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constexpr duration
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constexpr duration<rep, period>
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operator-() const
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{ return duration(-__r); }
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@ -0,0 +1,131 @@
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// Copyright (C) 2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-do compile { target c++11 } }
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// Test the changes introduced by P0548R1 "common_type and duration".
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// Specifically, duration<R,P>::period should be the reduced ratio,
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// and common_type<D1, D2>::type should be a duration using the
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// reduced ratio.
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#include <chrono>
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using std::chrono::duration;
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using std::ratio;
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using std::common_type;
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using std::is_same;
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void
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test01()
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{
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using D1 = duration<int, ratio<10, 10>>;
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static_assert( is_same<D1::period, ratio<1, 1>>::value,
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"duration<R, P>::period is P::type, not P" );
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using C1 = common_type<D1>::type;
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static_assert( is_same<C1, duration<int, D1::period>>::value,
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"common_type_t<duration<R, P1> is duration<R, P1::type>");
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static_assert( is_same<common_type<D1, D1>::type, C1>::value,
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"common_type_t<D1, D1> is common_type_t<D1>" );
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static_assert( is_same<common_type<D1, D1, D1>::type, C1>::value,
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"common_type_t<D1, D1, D1> is common_type_t<D1>" );
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using D2 = duration<int, ratio<30, 15>>;
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static_assert( is_same<D2::period, ratio<2, 1>>::value,
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"duration<R, P2>::period is P2::type, not P2" );
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using C2 = common_type<D2>::type;
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static_assert( is_same<C2, duration<int, D2::period>>::value,
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"common_type_t<duration<R, P2> is duration<R, P2::type>");
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static_assert( is_same<common_type<D2, D2>::type, C2>::value,
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"common_type_t<D2, D2> is common_type_t<D2>" );
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static_assert( is_same<common_type<D2, D2, D2>::type, C2>::value,
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"common_type_t<D2, D2, D2> is common_type_t<D2>" );
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using D3 = duration<int, ratio<4, 12>>;
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static_assert( is_same<D3::period, ratio<1, 3>>::value,
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"duration<R, P3>::period is P3::type, not P3" );
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using C3 = common_type<D3>::type;
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static_assert( is_same<C3, duration<int, D3::period>>::value,
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"common_type_t<duration<R, P3> is duration<R, P3::type>");
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static_assert( is_same<common_type<D3, D3>::type, C3>::value,
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"common_type_t<D3, D3> is common_type_t<D3>" );
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static_assert( is_same<common_type<D3, D3, D3>::type, C3>::value,
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"common_type_t<D3, D3, D3> is common_type_t<D3>" );
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using C12 = common_type<D1, D2>::type;
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static_assert( is_same<C12, C1>::value,
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"common_type_t<D1, D2> uses the right period" );
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using C21 = common_type<D2, D1>::type;
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static_assert( is_same<C21, C12>::value,
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"common_type_t<D1, D2> is common_type_t<D2, D1>" );
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using C13 = common_type<D1, D3>::type;
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static_assert( is_same<C13, C3>::value,
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"common_type_t<D1, D3> uses the right period" );
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using C31 = common_type<D3, D1>::type;
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static_assert( is_same<C31, C13>::value,
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"common_type_t<D1, D3> is common_type_t<D3, D1>" );
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using C23 = common_type<D2, D3>::type;
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static_assert( is_same<C23, C3>::value,
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"common_type_t<D2, D3> uses the right period" );
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using C32 = common_type<D3, D2>::type;
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static_assert( is_same<C32, C23>::value,
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"common_type_t<D2, D3> is common_type_t<D3, D2>" );
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using C123 = common_type<D1, D2, D3>::type;
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static_assert( is_same<C123, C3>::value,
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"common_type of three durations uses the right period" );
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using C132 = common_type<D1, D3, D2>::type;
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static_assert( is_same<C132, C123>::value, "order doesn't matter" );
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using C312 = common_type<D3, D1, D2>::type;
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static_assert( is_same<C312, C123>::value, "order doesn't matter" );
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using C321 = common_type<D3, D2, D1>::type;
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static_assert( is_same<C321, C123>::value, "order doesn't matter" );
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using C = common_type<duration<short, ratio<1, 3>>,
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duration<unsigned, ratio<1, 2>>>::type;
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static_assert( is_same<C, duration<common_type<short, unsigned>::type,
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ratio<1, 6>>>::value, "" );
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}
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void
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test02()
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{
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using D1 = duration<int, ratio<10, 10>>;
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D1 d1;
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static_assert( is_same<decltype(+d1), common_type<D1>::type>::value,
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"unary + returns the reduced duration" );
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static_assert( is_same<decltype(-d1), common_type<D1>::type>::value,
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"unary - returns the reduced duration" );
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using D2 = duration<int, ratio<30, 15>>;
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D2 d2;
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static_assert( is_same<decltype(+d2), common_type<D2>::type>::value,
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"unary + returns the reduced duration" );
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static_assert( is_same<decltype(-d2), common_type<D2>::type>::value,
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"unary - returns the reduced duration" );
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using D3 = duration<int, ratio<4, 12>>;
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D3 d3;
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static_assert( is_same<decltype(+d3), common_type<D3>::type>::value,
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"unary + returns the reduced duration" );
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static_assert( is_same<decltype(-d3), common_type<D3>::type>::value,
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"unary - returns the reduced duration" );
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}
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@ -31,4 +31,5 @@ void test01()
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}
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// { dg-error "must be a specialization of ratio" "" { target *-*-* } 0 }
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// { dg-prune-output "not a member" }
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// { dg-prune-output "'num' is not a member of 'int'" }
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// { dg-prune-output "'int' is not a class, struct, or union type" }
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