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From: dmitry@elros.cbb-automation.de (Dmitry A. Kazakov)
Newsgroups: comp.lang.ada
Subject: Re: Ada2005
Date: Tue, 18 Dec 2001 11:55:31 GMT
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On 17 Dec 2001 09:50:30 -0800, Ray Blaak <blaak@telus.net> wrote:

>dmitry@elros.cbb-automation.de (Dmitry A. Kazakov) writes:
>> However, what people criticizing Ada usualy want, is just a syntax
>> sugar, which would allow to refer methods using postfix form if there
>> is only one dispatching [or class-wide] argument and it is the first
>> one.
>
>Like me.
>
>> I think in a future revision there could be some variant of rename
>> statement which would allow to do this and also the opposite thing
>> [for "methods" of protected objects and tasks which are always called
>> using the postfix form]. For instance:
>> 
>> type Ellipse is tagged ...
>> procedure Draw (Figure : Ellipse, Where : Point);
>> entry Ellipse.Draw (Where : Point) renames Draw;
>
>Why not make it automatic? The extra declaration is tedious and requires extra
>maintenance.
>
>Given:
>
>  e : Ellipse;
>
>then have
>
>  e.Draw(p)
>
>be valid iff Draw exists with an Ellipse as its first parameter.

Maybe. Though, then you should allow funny constructions like:
e."abs", when function "abs" (X: Ellipse) return ... is defined. Also
you should support fully qualified forms like:

e.Geometry.Flat.Figures.Conic.Float_Figures.Ellipse.Draw (p);

>Then it is truly just an alternate syntax to be used if desired, and not used
>if not.
>
>Where it gets wierd, I suppose, is if one has an "in out" or "out"
>parameter. One wants to allow update methods, but does e.Draw(p) make sense if
>e is completely replaced?

Neither "in out" nor "out" mean that the argument is replaced. It
depends on by-copy vs. by-reference parameter passing mode. Though,
for tagged types by-reference is a requirement [to support redispatch,
I suppose (:-()].

procedure Draw (Figure : Ellipse, Where : Point); is an equivalent to
C++

virtual void Draw (Point Where) const;

procedure Draw (Figure : in out Ellipse, Where : Point); is an
equivalent to

virtual void Draw (Point Where);

Only for "out" C++ has no analogy. 

Regards,
Dmitry Kazakov