Re: [boost] Request For a feature - Templated virtual functions

Subject: Re: [boost] Request For a feature - Templated virtual functions
From: Ravi (lists_ravi_at_[hidden])
Date: 2009-02-11 17:26:30

On Wednesday 11 February 2009 13:27:46 Gokulakannan Somasundaram wrote:
>          As you all know, there are situations, wherein the virtual
> function usage can be replaced with templates. But virtual functions can
> never be used with templates, since all the instantiations have to be
> tracked to form the virtual function table. But we can ask the user to
> provide a typelist of classes, that would probably be used with the virtual
> template function. I think this would solve this issue for most of the
> cases.

If the list of arguments/return types is known at compile time, is this not 
the same as overloaded virtual functions? Here's an example:

#include <iostream>
using namespace std;
struct Base {
  virtual void func( int ) { cout << "Base::int overload" << endl; }
  virtual void func( double ) { cout << "Base::double overload" << endl; }
  template <typename T> void virtfunc( T x ) { func( x ); } // "virtual"
  virtual ~Base() {}
};
struct Derived : Base {
  virtual void func( int ) { cout << "Derived::int overload" << endl; }
  virtual void func( double ) { cout << "Derived::double overload" << endl; }
  virtual ~Derived() {} 
};

int main( int, char *[] ) {
  Base *p = new Derived;
  p->virtfunc( 3 );
  p->virtfunc( 3.14 );
}

$ g++ -o out -Wall tempvirt.cc
$ ./out
Derived::int overload
Derived::double overload

Regards,
Ravi