http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53000
Bug #: 53000
Summary: Trinary operator does not behave as standardized
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: gcc-b...@quasiparticle.net
The conditional operator as implemented in g++ from 4.7.0 (at least) onwards
does not behave as required by [expr.cond]p3 of the C++11 spec.
Given an expression "B ? E1 : E2", the result of the expression is required to
be an xvalue if E2 is an xvalue and E1 can be converted to T2&&. With E1 and E2
both being declval<int>(), the result should then be of type int&&, while g++
currently generates a plain int there.
Curiosly, this hides an oversight described in DR2141 [1], which reports the
common_type<T, U> trait as being defective. As soon as "true ? declval<int>() :
declval<int>()" yields int&& as required, common_type<int, int>::type of
libstdc++ will be int&& (is int right now). This will break <chrono> badly, as
experienced by clang++.
[1] http://cplusplus.github.com/LWG/lwg-active.html#2141
