From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2181) id 567F6388E81F; Tue, 17 Aug 2021 13:23:49 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 567F6388E81F MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jonathan Wakely To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r12-2956] libstdc++: Add conditional noexcept to std::exchange X-Act-Checkin: gcc X-Git-Author: Jonathan Wakely X-Git-Refname: refs/heads/master X-Git-Oldrev: 2db38d9fcacf522fe9b98ba847e79ba33abdcadc X-Git-Newrev: 42cfa1bd6c05f2dc0d6269155950d16064310f56 Message-Id: <20210817132349.567F6388E81F@sourceware.org> Date: Tue, 17 Aug 2021 13:23:49 +0000 (GMT) X-BeenThere: libstdc++-cvs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libstdc++-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 17 Aug 2021 13:23:49 -0000 https://gcc.gnu.org/g:42cfa1bd6c05f2dc0d6269155950d16064310f56 commit r12-2956-g42cfa1bd6c05f2dc0d6269155950d16064310f56 Author: Jonathan Wakely Date: Mon Aug 16 18:00:08 2021 +0100 libstdc++: Add conditional noexcept to std::exchange This is not required by the standard, but seems useful. Signed-off-by: Jonathan Wakely libstdc++-v3/ChangeLog: * include/std/utility (exchange): Add noexcept-specifier. * testsuite/20_util/exchange/noexcept.cc: New test. Diff: --- libstdc++-v3/include/std/utility | 2 ++ .../testsuite/20_util/exchange/noexcept.cc | 39 ++++++++++++++++++++++ 2 files changed, 41 insertions(+) diff --git a/libstdc++-v3/include/std/utility b/libstdc++-v3/include/std/utility index c2697f87dc5..69d274ff194 100644 --- a/libstdc++-v3/include/std/utility +++ b/libstdc++-v3/include/std/utility @@ -91,6 +91,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _GLIBCXX20_CONSTEXPR inline _Tp exchange(_Tp& __obj, _Up&& __new_val) + noexcept(__and_, + is_nothrow_assignable<_Tp&, _Up>>::value) { return std::__exchange(__obj, std::forward<_Up>(__new_val)); } #if __cplusplus >= 201703L diff --git a/libstdc++-v3/testsuite/20_util/exchange/noexcept.cc b/libstdc++-v3/testsuite/20_util/exchange/noexcept.cc new file mode 100644 index 00000000000..6363a4d4c06 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/exchange/noexcept.cc @@ -0,0 +1,39 @@ +// { dg-options "-std=gnu++2a" } +// { dg-do compile { target c++2a } } + +#include + +// This is a GCC extension. std::exchange is not required to be noexcept. + +static_assert( noexcept( std::exchange(std::declval(), 1) ) ); + +struct X +{ + X(const X&); + X(X&&) noexcept; + X& operator=(const X&); + X& operator=(X&&) noexcept; + X& operator=(int); +}; + +extern X x, x2; +static_assert( noexcept( std::exchange(x, std::move(x2)) ) ); +static_assert( ! noexcept( std::exchange(x, 1) ) ); + +struct Y +{ + Y(Y&&) noexcept; + Y& operator=(Y&&); +}; + +extern Y y, y2; +static_assert( ! noexcept( std::exchange(y, std::move(y2)) ) ); + +struct Z +{ + Z(Z&&)noexcept; + Z& operator=(Z&&) ; +}; + +extern Z z, z2; +static_assert( ! noexcept( std::exchange(z, std::move(z2)) ) );