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Date: Mon, 18 Dec 2017 07:34:48 -0800 (PST)
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Subject: Re: how to do things like procedure foo(A: string) is bar: string :=
 A; begin; ...;end;
From: Mehdi Saada <00120260a@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:49515
Date: 2017-12-18T07:34:48-08:00
List-Id: <comp.lang.ada>

I got it pretty early (was clear in the course) that array, and strings for the matter, can have arbitrary bounds. So with unconstrained formal parameters I always use 'LENGHT, 'First and 'Last, and no 'Range in for loop.
But your "" & S was mind-boggling... It does have the effect of changings bounds without touching the content. Very useful, thanks !
Not sure about the constrained formal parameter part. What happens when you call something like
function FOO(T: String range 5..9) return String;
with a parameter whose index subtype's bounds are say, 1..4 ? You say it would raise Constraint_Error ? If so I can see the point. There's never too much facultative checks.