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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Constraints in extended return
Date: Sat, 19 Mar 2011 09:30:18 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2011-03-19T09:30:18-04:00
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Simon Wright <simon@pushface.org> writes:

> This is all very well for providing a value where no constraint is
> otherwise imposed, for example as an actual in a subprogram call, but
> what about the case where there is a prior constraint?

You get Constraint_Error if the constraint is wrong.
But this isn't directly related to extended return statements.
You get the same thing for old-fashioned returns:

    function F(...) return String is
    begin
        ...
        return "Hello";
    end F;

    X : String (1..100);

    X := F(...); -- Constraint_Error

> Is there any way for the extended return to determine the constraints of
> the 'target'?

No.  You can do that for 'out' parameters, but unfortunately not for
function results.  So normally, you would avoid constraining at
the call site, and do things like:

   Output : constant Complex_Matrix := Transpose (Input);

- Bob