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From: Chris Powell <chris.powell@rrds.co.uk>
Subject: Re: Help me to chose between ADA 95 and C++
Date: 1999/12/23
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Date: 1999-12-23T10:28:39+00:00
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Stephen Leake wrote:
 
> Hmm. I don't see why Dispatching_Method should _want_ to re-dispatch.
> You could simply override Dispatching_Method, in addition to
> Another_Dispatching_Method. Can you give a good example of when this
> is not a good idea?

My example was too simple. In reality, Dispatching_Method would perform
some other functionality as well as calling Another_Dispatching_Method.
Overriding Dispatching_Method would mean this behaviour would need to be
reimplemented in the derived class, probably via cut and paste.
 
> > Passing 'This' as an access parameter is common (since references to
> > objects are often stored by an object, but further complicates the
> > syntax.
> 
> No problem here. The syntax is complicated (I assume you are refering
> to "Object'Class (This.all)'Access") because you are doing things the
> hard way; just override Dispatching_Method.

No, I only write the same bit of code once: in the base class.

> In Ada, you have complete control over whether a call dispatches or
> not. If the actual parameter is class-wide, you get dispatching.
> Otherwise, you get static binding. Static binding is a Good Thing in
> some situations; I'm not clear you ever get it in C++.

Yes C++ has both. The difference is that C++ uses dynamic binding by
default and Ada uses static.
 
> C++ uses "object.method". Ada uses Method (object). Same logical
> association. Hmm, if you have more parameters, and don't put the
> object first in Ada, you might lose something. Once again, Ada gives
> you a choice, C++ doesn't.

C++ does allow binary methods which are defined outside a class, so in
fact it is C++ which gives you the choice, and Ada which does not.

Chris.