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Generalizing Mixins... c++'03

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Hi All,

I've recently used mixins (without the courtesy of 
compilers supporting variadic templates) and were 
irritated by the fact that one had to always implement 
many constructors (one per base):

Definition of Mixin: courtesy of http://www.drdobbs.com/cpp/184404445

A mixin is a fragment of a class that is intended to be composed with other classes or mixins...

For the problem I've come up with this solution (amongst others).

What do you think?


//////////////////////////////////////
#include <iostream>
 
struct Base
{
  Base();
  Base( int i, int j ){}
  virtual void foo()
  {
    std::cout << "Base::foo()" << std::endl;
  }
};
 
template <class BaseT>
struct Mixin : virtual BaseT
{
  typedef BaseT base_type;
  //Problem
  //-Which constructor...? Always default... Generic!
 
  //Adds foo to any Base...
  virtual void foo()
  {
    std::cout << "Derived::foo()" << std::endl;
  }
};
 
//Solution? Something that calls base 
// constructor directly-always...
 
template <class MixinT>
struct GenMixin : 
  virtual MixinT::base_type,
  MixinT
{
  typedef typename MixinT::base_type base_type;
  GenMixin()
  {
  }
  template <class A0>
  GenMixin( A0 a0 )
  : base_type( a0 )
    //Mixin always has default only...
  {
  }
  template <class A0, class A1>
  GenMixin( A0 a0, A1 a1 )
  : base_type( a0, a1 )
    //Mixin always has default only...
  {
  }
};
 
typedef GenMixin<Mixin<Base> > MyMixin;
int main()
{
  MyMixin( 1, 2 ).foo();
}

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Generalizing Mixins... c++'03 Werner <werasm@gmail.com> - 2012-04-18 07:21 -0700
  Re: Generalizing Mixins... c++'03 Werner <werasm@gmail.com> - 2012-04-19 01:04 -0700

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