Shadowing in template template function within class template.

["Rodolfo Federico Gamarra" <rgamarra at gmail dot com>]

Hi all!

I have a question about the diagnosis and resolution of template
arguments, in a situation which aborts the compilation. The problem
itself can be bypassed easily.

I'm using g++ (GCC) 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)

I have a template template function in three different contexts:
    (I)   As a member of a template class.
    (II)  As a member of class.
    (III) As a plain function.

The template argument declaration for it may be
  template <class R, template<class S> class T >
if the declaration is changed to
  template <class R, template<class R> class T >
then the upon compilation the result is
  error: declaration of 'class R'
  error:  shadows template parm 'class R'
only in case (I).

In can't see the reason why there are different diagnoses depending on
the context (I, II or III). As of item 3 of 14.6.1 ("Locally declared
names") of The Standard hidding is ocurring in all three cases:

"The scope of a template-parameter extends from its of declaration
until the end of its template. A template-parameter hides any entity
with the same name in the enclosing scope."

I have put an example at the end of the email.

Thanks a lot for your help.

--
Rodolfo Federico Gamarra

// Dummy template class.
template<class> class A { };
// Template class with templated member function.
template<class> class B {
  public:
/*
  template <class R,
    template<class R> //--> shadows. Doesn't compile.
      class T >
//main.cc:8: error: declaration of 'class R'
//main.cc:7: error:  shadows template parm 'class R'
*/
/**/
  template <class R,
    template<class S>
      class T >
/**/
  void f(T<R> a) { }
};
// Class with template member function.
class C {
  public:
  template <class R,
    template<class R> // this doesn't shadow. Compiles 0k.
      class T >
  void f(T<R> a) { }
};
// Function template.
template <class R,
  template<class R> // this doesn't shadow. Compiles 0k.
    class T>
void f(T<R>& a) { }

int main()
{
  A<int> a;
  B<int> b;
  C c;
  b.f(a);
  c.f(a);
  f(a);
}