TITLE: member function templates


PROBLEM: patrick@zaphod.ruhr.de (Patrick Halke)

Can somebody tell me why templates of member functions are not allowed ?

For instance something like this:

template<class T>
class Foo {

  template<class U>
  T FooFunc(U u)
  {
    return (T)u;   // :)
  }
};


RESPONSE: clamage@Eng.Sun.COM (Steve Clamage), 3 Jun 95

When the template mechanism was being designed, there was concern
about the effect of member templates. No one knew (since there were
no implementations and no experience) what dangers there might be.
It is easier to relax a restriction than to remove a language
feature, so member templates were disallowed.

After some experience, it is now known that member function
templates for non-virtual functions do not cause problems. The
language specification has been changed to allow them. It may
be a while before compilers supporting this feature are
widely available.

Virtual functions cannot be member templates, since there would
be no way to know at compile time how many different virtual
functions would eventually be generated. (The implemenation isn't
impossible, but would be very difficult on most systems, and
increase program build times.)