When does overload resolution of non-dependent name take place, in definition context or point of instantiation?

问题

3.4 [basic.lookup]/p1

Overload resolution (13.3) takes place after name lookup has succeeded.

void g(long);

void g(int, int);

template<class T> void f() { g(0); }

void g(int, int = 0) {}

int main(){
    f<int>();
}

gcc compiles succeed, clang faild.

When does overload resolution of non-dependent name take place, in definition context or point of instantiation? Or both are right?

回答1:

In both context.

[temp.res] 14.6\8

If a hypothetical instantiation of a template immediately following its definition would be ill-formed due to a construct that does not depend on a template parameter, the program is ill-formed; no diagnostic is required. If the interpretation of such a construct in the hypothetical instantiation is different from the interpretation of the corresponding construct in any actual instantiation of the template, the program is ill-formed; no diagnostic is required.

[temp.nondep] 14.6.3\1

Non-dependent names used in a template definition are found using the usual name lookup and bound at the point they are used.

So both compilers are right.

回答2:

If my understanding of the lookup rules are correct, then since g() is a non-dependent name, the overload set won't be added to in phase 2. Therefore the only choice for g(0) at the point of definition is g(long), and Clang is correct.

I would certainly naively expect only g(long) to be considered given the ordering of the definitions, but then again the C++ standard isn't always intuitive when templates are involved...

来源：https://stackoverflow.com/questions/34154770/when-does-overload-resolution-of-non-dependent-name-take-place-in-definition-co