Question on visible scope in template declaration

[Andrew Pinski]

On Mon, Dec 14, 2015 at 7:01 PM, Carl Lei <xecycle@gmail.com> wrote:
> Hello list,
>
> The following code is rejected by GCC but accepted by Clang:
>
> template <class T>
> auto f(T v) -> decltype(g(v));
>
> int g(int) { return 0; }
>
> template <class T>
> auto f(T v) -> decltype(g(v))
> {
>   return g(v) + 1;
> }
>
> int main()
> {
>   return f(0);
> }
>
> Error message at http://ideone.com/Vn79Hm.
>
> Basically the problem comes down to which is the visible scope in that
> trailing return type decltype(g(v)), where GCC uses the point of declaration
> but Clang uses the point of definition.  g is a dependent name here, and the
> standard says "template definition context" should be used; but I am not
> very sure about the wording.  I suspect this to be a GCC bug, but not sure,
> so asking here first.

There is also argument dependent lookup.

Thanks,
Andrew Pinski

>
> --
> Carl Lei (XeCycle)
> Department of Physics and Astronomy, SJTU