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From: mheaney@on2.com (Matthew Heaney)
Newsgroups: comp.lang.ada
Subject: Re: Two class-wide operands, but only one controlling
Date: 27 Nov 2002 09:25:29 -0800
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porton@ex-code.com (Victor Porton) wrote in message news:<3de0b9be$0$304$bed64819@news.gradwell.net>...
> 
> Not what I need. basically I have a container and an iterator.
> Both a derived (in my case I need this) from abstract container
> and abstract iterator. I need procedure like:
> 
> procedure Next
>   (C: Abstract_Container'Class; I: in out Abstract_Iterator'Class);
>   
> but this is an error as we have two controlling operands of
> different types :-( I cannot make one of these non class-wide
> as both a abstract.
> 
> It was simple in C++. Ada has disadvantages...

A virtual function can only be a class member function, which means it
can be virtual for only one class.

Either you have this:

class Container
{
public:
   class Iterator { ... };

   virtual void next(Iterator&) const = 0;
...
};

Or you have this:

class Container
{
public:
   class Iterator 
   {
   public:
      virtual void next(const Container&) = 0;
      ...
   };
...
};


Both of which have a trivial conversion to Ada95.  So what is the
problem, exactly?