Explicitly instantiating a generic member function of a generic structure

I have a structure with a template parameter, Stream. Within that structure, there is a function with its own temp开发者_运维百科late parameter, Type.

If I try to force a specific instance of the function to be generated and called, it works fine, if I am in a context where the exact type of the structure is known. If not, I get a compile error. This feels like a situation where I'm missing a typename, but there are no nested types. I suspect I'm missing something fundamental, but I've been staring at this code for so long all I see are redheads, and frankly writing code that uses templates has never been my forte.

The following is the simplest example I could come up with that illustrates the issue.

#include <iostream>

template<typename Stream>
struct Printer {
  Stream& str;
  Printer(Stream& str_) : str(str_) { }

  template<typename Type>
  Stream& Exec(const Type& t) {
    return str << t << std::endl;
  }
};

template<typename Stream, typename Type>
void Test1(Stream& str, const Type& t) {
  Printer<Stream> out = Printer<Stream>(str);
  /****** vvv This is the line the compiler doesn't like vvv ******/
  out.Exec<bool>(t); 
  /****** ^^^ That is the line the compiler doesn't like ^^^ ******/
}

template<typename Type>
void Test2(const Type& t) {
  Printer<std::ostream> out = Printer<std::ostream>(std::cout);
  out.Exec<bool>(t);
}

template<typename Stream, typename Type>
void Test3(Stream& str, const Type& t) {
    Printer<Stream> out = Printer<Stream>(str);
    out.Exec(t);
}

int main() {
  Test2(5);
  Test3(std::cout, 5);
  return 0;
}

As it is written, gcc-4.4 gives the following:

test.cpp: In function 'void Test1(Stream&, const Type&)':

test.cpp:22: error: expected primary-expression before 'bool'

test.cpp:22: error: expected ';' before 'bool'

Test2 and Test3 both compile cleanly, and if I comment out Test1 the program executes, and I get "1 5" as I expect. So it looks like there's nothing wrong with the idea of what I want to do, but I've botched something in the implementation.

If anybody could shed some light on what I'm overlooking, it would be greatly appreciated.

You need to tell the compiler that the dependent name Printer<Stream>::Exec is a template:

out.template Exec<bool>(t);

It's the same principle as with typename, just that in this case the problematic name is not a type, but a template.