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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada Interfaces and the Liskov Substitution Principle
Date: Thu, 24 May 2007 17:58:23 -0500
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Date: 2007-05-24T17:58:23-05:00
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"Maciej Sobczak" <see.my.homepage@gmail.com> wrote in message
news:1180011507.159515.46920@o5g2000hsb.googlegroups.com...
...
> I was talking about real assignment - and this assumes that two
> objects already exist and we make one to be equal to the other. There
> is no way to do it right.

(Using the *correct* terminology as Bob noted)

Given the current Ada rules, what classwide assignment is good for is
*re*construction:

     procedure Do_Something(Y : out Object'Class) is
     begin
         Y :=  Constructor_Func (<some details of Y>);
     end Do_Something;

that is, the replacement of an object with different one of the same type.
The Constructor_Func is dispatching on the real type of the LHS object, so
the new object will be constructed with the proper attributes of that type.
Admittedly, this is not a common need, although I think I used it once in
the Claw builder to change properties on the fly that Claw doesn't support
changing on the fly. (Ultimately, though, we changed Claw to be more
flexible.)

                                          Randy.