From f0f04e1dffea609cb74ac0b488385401ed7e15a3 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Wed, 24 Aug 2022 00:10:59 +0100 Subject: [PATCH] libstdc++: Add check for LWG 3741 problem case This LWG issue was closed as NAD, as it was just a bug in an implementation, not a defect in the standard. Libstdc++ never had that bug and always worked for the problem case. Add a test to ensure we don't regress. The problem occurs when abs is implemented using a ternary expression: return d >= d.zero() ? d : -d; If decltype(-d) is not the same as decltype(d) then this is ambiguous, because each type can be converted to the other, so there is no common type. libstdc++-v3/ChangeLog: * testsuite/20_util/duration_cast/rounding.cc: Check abs with non-reduced duration. --- libstdc++-v3/testsuite/20_util/duration_cast/rounding.cc | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/libstdc++-v3/testsuite/20_util/duration_cast/rounding.cc b/libstdc++-v3/testsuite/20_util/duration_cast/rounding.cc index af6e72d9e2eb..c5179b6eb6e2 100644 --- a/libstdc++-v3/testsuite/20_util/duration_cast/rounding.cc +++ b/libstdc++-v3/testsuite/20_util/duration_cast/rounding.cc @@ -58,3 +58,8 @@ static_assert( std::chrono::round(2501ms) == 3s ); static_assert( std::chrono::abs(100ms) == 100ms ); static_assert( std::chrono::abs(-100ms) == 100ms ); + +// LWG 3741. std::chrono::abs(duration) is ill-formed with non-reduced periods +using D1000 = std::chrono::duration>; +static_assert( std::chrono::abs(D1000(-2)) == D1000(2) ); +static_assert( std::is_same_v ); -- 2.47.2