Dependant names

Using a template argument as a template argument for something else sometimes doesn't work, for example the following code:

#include <iostream>

using namespace std;

template<class _prec=double>
class myclass {
  public:

   typedef int atype;
};

template<class _prec=double>
class myclass2 {
  public:

  _prec method() {
    myclass<_prec>::atype t = 0;
    return t;
  }
};

int main() {

  myclass2<> m;

}

Gives this compilation error under g++:

templateargasarg.cpp: In member function '_prec myclass2<_prec>::method()':
templateargasarg.cpp:17: error: expected `;' before 't'
templateargasarg.cpp:18: error: 't' was not declared in this scope

It's something to do with dependant names, google it. I don't fully understand it. All I know is that as usual a typename fixes it i.e.:

    myclass<_prec>::atype t = 0;

becomes:

   typename myclass<_prec>::atype t = 0;

and all is well. My comp.lang.c++ thread is here.