This is the mail archive of the gcc-help@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: std::experimental::optional::swap() vs std::swap()




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?


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]