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From: "Marin D. Condic" <mcondic-nospam@quadruscorp.com>
Subject: Re: Learning Ada & a question
Date: 2000/04/11
Message-ID: <38F35993.7A84BF3F@quadruscorp.com>#1/1
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Organization: Quadrus Corporation
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Newsgroups: comp.lang.ada
Date: 2000-04-11T13:59:36+00:00
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G wrote:
> 
> In C++ they have devised all these ingenious little techniques for
> getting more than one return value from a function.  I am just wrapping
> my mind around the notion of pass-by-reference with pointers and
> references.  I know that access types are a sort of pointer in Ada.  Can
> you do the same things in Ada ?  Do you need to when Procedures can be
> called just as easily as functions anyways and return as many things as
> you need ?  (I maybe didnt say that right).
> 
I think what you're asking is "Can functions in Ada have 'out'
parameters so that more than just the function result can be returned?"
The short answer is 'no'. C/C++ never developed the notion of a
"procedure" which does not return a single result and cannot be used in
an equation. They sort of tacked that on by creating void functions and
having you pass the address of parameters (or ref in C++).

If you need something that computes multiple values and returns multiple
results, the correct way to do that in Ada is with a procedure. You
can't use a procedure in an equation, specifically because it doesn't
return a single result. If for some reason (and those reasons are rare)
you need a function that returns a single result and then has side
effects on its parameters, there is something called "The Rosen Trick"
which you can find on www.adapower.com or on my web site. (See below). I
would *strongly* advise avoiding this as a general programming technique
since it violates the general intent of the language, but it does have
its place.

If you want to get multiple results for a calculation, the way to do it
is basically like this:

procedure Get_Three_Results (X, Y, Z : out Integer) is.....

...

Get_Three_Results (A, B, C) ;
K := A + B + C ;

.....


Hope this is helpful

MDC
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Marin David Condic - Quadrus Corporation - http://www.quadruscorp.com/
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