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Newsgroups: comp.lang.ada
From: Ted Dennison<dennison@telepath.com>
References: <3BD91EF8.EEB7EDBA@systems.saab.se>
Subject: Re: When to do a constraint check and not ??
Message-ID: <2heC7.1440$xS6.1918@www.newsranger.com>
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NNTP-Posting-Date: Fri, 26 Oct 2001 10:18:38 EDT
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Date: Fri, 26 Oct 2001 14:18:38 GMT
Xref: archiver1.google.com comp.lang.ada:15246
Date: 2001-10-26T14:18:38+00:00
List-Id: <comp.lang.ada>

In article <3BD91EF8.EEB7EDBA@systems.saab.se>, Per Sandberg says...
>
>Assume the folowing code:
>
>procedue bla is
>	b : boolean; --< B may contain any bit pattern at this point.
>
>	procedure test( p : in out boolean ) is
>	begin
>		b := false;
>	end test;
>
>begin
>	test(b); --<< Is the compiler allowed to insert a constraint check on b
>here ??
>end;

I don't see why it wouldn't be allowed to. It seems quite sensible to want to
verify the object before it is read. Reading the variable is what you are saying
will happen in your routine when you give the parameter a mode designator of
"in". 

In this example, there's really no reason why your parameter needs to be "in
out". Even if you had extra code in there that, say, tried to read "b" later on
in "test", you could have used mode "out". The only reason you could possibly
need "in out" is if you might want to read the value inside of "test" *before*
test writes to it. That would clearly only be valid if a valid value is passed
in, and in that case you definitely *want* the constraint check (and probably
want it where they placed it).

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

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