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From: Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: OO in Ada
Date: Tue, 8 Oct 2002 23:18:41 +0200
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Date: 2002-10-08T23:18:41+02:00
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Matthew Heaney wrote:

> "SteveD" <nospam_steved94@attbi.com> wrote in message
> news:JVrn9.40015$FO4.9224@sccrnsc03...
>>
>> In C++ there is a hidden "this" pointer quietly hiding in the background
>> that you must be very much aware of (if you're doing any serious
>> programming).  In Ada this is an explicit variable passed into the
>> procedure.
> 
> This is also true in Ada, wrt passing unconstrained arrays:
> 
> procedure Op (S : String) is
> 
> You're actually passing a descriptor on the stack, which contains info
> about
> the string's length and index range.  So here there is "hidden"
> information being passed too, not unlike an implicit this-ptr in C++.

There are other examples where Ada follows this approach: protected objects 
and tasks. They do have prefix syntax of entry point calls and a hidden 
parameter:

task type A is
   entry Do_It;
end A;
...
X : A;
...
X.Do_It; -- X is a hidden parameter

Same as with C++, this approach works no longer a subroutine has exactly 
one "special" parameter. For example, should we allow in Ada rendezvous 
with several tasks, then the prefix syntax should be replaced by explicit 
parameter passing:

task type A;
task type B;
entry Do_It (X : in out A; Y : in out B); -- This is not Ada!
...
X : A; Y : B;

Do_It (X, Y); -- This is not Ada!

-- 
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de