CODEWITHSUNDEEP
c++templateslanguage-lawyerfunction-templates
user19414420
user19414420

Reputation:

Function template argument deduction works in gcc but not in msvc and clang

I am learning C++ templates using the resource listed here. In particular, read about template argument deduction. Now, after reading, to further clear up my concept of the topic I tried the following example that compiles in gcc but not in clang and msvc. Demo

template<typename T = int> void f()
{

}
template<typename T> void func(T)
{

}
int main()
{
    func(f); //works in gcc but not in clang and msvc 
    func(f<>); //works in all
}

As we can see, the above example compiles fine in gcc but not in clang and msvc. My question is which compiler is right here according to the latest standard?

Upvotes: 2

Views: 140

Answers (1)

user12002570
user12002570

Reputation: 1

This is CWG 2608 and the program is well-formed so that gcc is correct in accepting the program.

From temp.arg.explicit#4 which was added due to cwg 2608, the default template argument can be used and the empty template argument list <> can be omitted.

If all of the template arguments can be deduced or obtained from default template-arguments, they may all be omitted; in this case, the empty template argument list <> itself may also be omitted.

(emphasis mine)

Note the bold highlighted part in the above quoted statement, which means that the empty template argument list <> can be omitted in your example because all of the template arguments can be obtained from default template-arguments.

Further, over.over#3 can also be used here to see that the specialization generated from temp.arg.explicit is added to the overloaded set:

The specialization, if any, generated by template argument deduction ([temp.over], [temp.deduct.funcaddr], [temp.arg.explicit]) for each function template named is added to the set of selected functions considered.

(emphasis mine)

This means that at the end, the call func(f); is well-formed and uses the generated specialization f<int>.

Upvotes: 2

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