template<bool param> class T
{
public:
  int data_field;
  void some_method()
  {
    if(param)
      data_field++;
    else
      data_field--;
  }
};

class U
{
public:
  union
  {
    int data_field;
    T<true> on_true;
    T<false> on_false;
  };

  C(int value)
  {
    data_field = value;
  }

  ~C()
  {
    data_field = 0;
  }

  void do_some(bool target)
  {
    if(target)
      on_true.some_method();
    else
      on_false.some_method();
  }
};

template<bool param> class T> {
> public:
>   int data_field;
>   void some_method()
>   {
>     if(param)
>       data_field++;
>     else
>       data_field--;
>   }
> };

template<bool param> class T> > {
> > public:
> >   int data_field;
> >   void some_method()
> >   {
> >	 if(param)
> >	   data_field++;
> >	 else
> >	   data_field--;
> >   }
> > };

class U
{     int data_field;
      void some_method(bool param)
      {     if(param)   data_field++;
            else
            data_field--;
      }
      friend class A; // или
      friend void classB::SomeMetod( );
 };