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?
