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From: joeuser@satcom.whit.org (joeuser)
Subject: Re: Concerning subscript bounds checks
Date: 1996/06/28
Message-ID: <4r1aep$7ga@natasha.rmii.com>#1/1
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references: <4qdj3e$btf@goanna.cs.rmit.EDU.AU> <dewar.835402601@schonberg>
 <4ql9eq$hdt@goanna.cs.rmit.EDU.AU>
content-type: Text/Plain; charset=US-ASCII
organization: Satcom
keywords: subscripts
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newsgroups: comp.lang.ada,comp.lang.misc
Date: 1996-06-28T00:00:00+00:00
List-Id: <comp.lang.ada>

I think I have the right piece of text here.


        >The remaining 4 occur in this context:
        >    subtype Simplex_Range is Natural range 0 .. Point'Length;
        >    P: "array (Simplex_Range) of ..."
        >    Y: "array (Simplex_Range) of ..."
        >    X: Point;
        >    J: Simplex_Range;
        >    ...
        >    J := 0;            -- at the start, J = Simplex_Range'First
        >    for I in X'Range loop
        >       ...
        >       P(J) := ...
        >       Y(J) := ...
        >       J := J + 1;
        >    end loop;          -- at the end, J = Simplex_Range'Last
        >    P(J) := ...
        >    Y(J) := ...
        >end;

        >A reasonably smart compiler should be able to tell that these four
        >subscripts are also safe.


and this is intuitively obvious to the most casual observer?
 
I think not.

Your problem lies in the J:=J+1; statement

You would be better off to use I as your index and not J.  (and it would work 
too.)  Here is why.

What happens the first time through this loop?

I=0
J=0

BUT guess what!!!!
J:=J+1;

That means that when I=X'Last
J will become X'Last+1

This basically equates to Simplex_Range'Last+1
                 Hence-----> your constraint error

J is now out of all it's possible ranges (and the ranges for the subscripts 
for both P and Y.

Is Point a string????

I love to bitch at the compilers too, but they are never wrong.  They cannot 
be wrong because they meet their standards.  Now WE have to meet theirs.

I just hope I got this to the right person.  I don't have the original 
message and had to kind of make this up from fragments.