What should `foo.template bar()` do when there's both a template and a non-template overload?

user_2752075 0
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A coworker shared this code with me:

run on gcc.godbolt.org

#include <iostream>

struct A
{
    void foo() {std::cout << "1\n";}
    
    template <typename T = int>
    void foo() {std::cout << "2\n";}
};

int main()
{
    A x;
    x.template foo();
}

GCC prints 1, Clang prints 2, and MSVC complains about missing template arguments.

Which compiler is correct?

language-lawyer c++
2 Answers

[temp.names]/5 says that a name prefixed by template must be a template-id, meaning that it must have a template argument list. (Or it can refer to a class/alias template without template argument list, but this is deprecated in the current draft as a result of P1787R6 authored by @DavisHerring.)

There is even an example almost identical to yours under it, identifying your use of template as ill-formed.

The requirement and example comes from CWG defect report 96, in which the possible ambiguity without the requirement is considered.

Open GCC bug report for this is here. I was not able to find a Clang bug report, but searching for it isn't that easy. Its implementation status page for defect reports however does list the defect report as unimplemented.

user_177325220

MSVC is correct to reject this: the standard has just this as an example. The template parser guide is allowed before the qualified name of a class or alias template without template arguments, but this is only for compatibility with implementations that needlessly require it for template template arguments and is now deprecated.

user_85862270
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