Why do I get an error trying to call a template member function with an explicit type parameter?

Question

I don't get it, it seems to me that the call to f is completely unambiguous, but it fails to compile with expected primary-expression before ‘int’. If I comment out the line with the call to f, it compiles fine.

template<typename T> struct A {     template<typename S>     void f() { } };  template<typename T> struct B : A<T> {     void g() {         this->f<int>();     } }; 

Answer 1

This is due to a really obscure provision of the standard in which if you have a template that tries to access a template function in an object whose type depends on a template argument, you have to use the template keyword in a weird way:

this->template f<int>(); 

This is similar to the weirdness with typename that comes up with dependent types, except as applied to functions. In particular, if you leave out the template keyword, there's a parsing ambiguity between

this->f<int>() 

(what you intended), and

((this->f) < int) > () 

which makes no sense (hence your error). The use of the keyword template here disambiguates and forces the compiler to recognize that it's looking at a perfectly valid call to a templated member function rather than a garbled mass of symbols.

Hope this helps!