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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Certified C compilers for safety-critical embedded systems
Date: Wed, 07 Jan 2004 14:39:54 +0100
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On Wed, 07 Jan 2004 12:56:36 GMT, Marin David Condic
<nobody@noplace.com> wrote:

>What exactly would be the meaning of:
>
>A := Func_X (A) + Func_Y (A) ;
>
>if functions had in-out parameters and A could be modified while 
>evaluating the RHS? I suppose one might be able to come up with some 
>evaluation rules that at least meant determinism for the end result, but 
>staring at it would not make it intuitively obvious to even the most 
>casual observer. Sure, the functions *could* modify A if they had 
>visibility to the right scope, but how often does someone do that in 
>real-world use? The current style - while not guaranteeing a lack of 
>side effects - tends to discourage it and leads to more easily 
>comprehended code.
>
>I don't understand what the headache is here anyway. If one wants to 
>modify parameters, use a procedure. If one wants some kind of 
>math-oriented thingie to return a result, use a function.

The headache is:

declare
   X : Y'Class := <no procedure allowed here!>;
   Z : String := <no procedure allowed here!>;

One wants:

A. to have an ability to return objects of unconstrained types
B. in design, to avoid side-effects not manifested by the parameters
C. in design, to avoid unnecessary use of pointers

A+B+C is that too much?

[ In any of the possible evaluation orders? I have an impression that
some people would agree with A, B, C, but not with A+B+C (:-)) ]

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