Re: Partial specialisation

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Thu, 17 May 2007 09:37:48 -0400

Message-ID:

<f2hlrd$i04$1@news.datemas.de>

Alan Woodland wrote:

The following code is legal, and works as expected:

#include <iostream>

template <typename T>
class Bar {
};

template <typename T, typename P>
class Foo {
public:
  void doStuff();
};

template <typename T, typename P>
void Foo<T, P>::doStuff() {
  std::cout << "General" << std::endl;
}

int main() {
  Foo<float, Bar<float> > a;
  a.doStuff();

  Foo<float, float> b;
  b.doStuff();

  return 0;
}

But none of these specialise the method doStuff():

// Not valid:
template <typename T>
void Foo<T, Bar<T> >::doStuff() {
  std::cout << "Specific" << std::endl;
}

// Not valid:
template <typename T, typename P=Bar<T> >
void Foo<T, P>::doStuff() {
  std::cout << "Specific" << std::endl;
}

// Not valid:
template <typename T, Bar<T> >
void Foo<T, Bar<T> >::doStuff() {
  std::cout << "Specific" << std::endl;
}

Is there a valid way to achieve this without using a non member
template function and calling that from within the generic doStuff()?

No. What you're attempting to do here is to create an _implicit_
partial specialisation of a class template through defining a single
member of it (and without defining the actual partial specialisation
of the class template). That's impossible. You need to define the
entire class template (by repeating most of it) and then define the
member that is different from the unspecialised template.

V
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