Vararg templates. GCC vs Clang

Sat Feb 7 00:05:00 GMT 2015

On 6 February 2015 at 12:12, Victor <d.v.a@ngs.ru> wrote:
>
>
>
>   --- the forwarded message follows ---
>
>
> ---------- Forwarded message ----------
> From: Victor <d.v.a@ngs.ru>
> To: gcc-help@gcc.gnu.org
> Cc:
> Date: Wed, 04 Feb 2015 15:41:56 +0600
> Subject: Vararg templates. GCC vs Clang
> Code:
>
> #include<tuple>
> #include<iostream>
>
> template<class Head, class... Tail>
> void f(std::tuple<Head, Tail...> )
> {
>     std::cout << "std::tuple<Head, Tail...>\n";
> }
>
> template<class Head>
> void f(std::tuple<Head> )
> {
>     std::cout << "std::tuple<Head>\n";
> }
>
> int main()
> {
>     f(std::tuple<int>{});
> }
>
> GCC accepts this code silently. But Clang generates error:
>
> test.cpp:18:5: error: call to 'f' is ambiguous
>     f(std::tuple<int>{});
>     ^
> test.cpp:5:6: note: candidate function [with Head = int, Tail = <>]
> void f(std::tuple<Head, Tail...> )
>      ^
> test.cpp:11:6: note: candidate function [with Head = int]
> void f(std::tuple<Head> )
>      ^
>
> Which compiler is right? Isn't it abiguity in fact?

This question would have been more appropriate on the gcc-help mailing list.

Technically the standard says it's ambiguous, but the C++ committee
believes that to be a defect and plan to fix it, see
http://open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1395