On 04/22/2017 11:34 PM, Jonathan Wakely wrote:
On 22 April 2017 at 20:24, Avi Kivity wrote:libstdc++'s optional::swap reads as follows: void swap(optional& __other) noexcept(is_nothrow_move_constructible<_Tp>() && noexcept(swap(declval<_Tp&>(), declval<_Tp&>()))) { When compiling with clang, it complains that swap() (called from the noexcept operator) accepts only one argument. Isn't it correct? shouldn't single-argument member swap() hide the two-argument non-member swap? A few lines below, libstdc++ continues: using std::swap; if (this->_M_is_engaged() && __other._M_is_engaged()) swap(this->_M_get(), __other._M_get()); else if (this->_M_is_engaged()) { __other._M_construct(std::move(this->_M_get())); this->_M_destruct(); } else if (__other._M_is_engaged()) { this->_M_construct(std::move(__other._M_get())); __other._M_destruct(); } } So it's explicitly bringing std::swap into scope here, but it's too late for the expression in the noexcept operator. Is this a bug in libstdc++ (and in gcc for not detecting it), or in clang?Yes, it's a libstdc++ bug, similar to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63860 It's a G++ bug for not detecting it (we do lookup in exception specifications incorrectly). We have __is_nothrow_swappable now, so should be using that there, could you report it to bugzilla please?
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80493 Shall I file a bug for the incorrect lookup as well?
