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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Contraint error when "out" parameter has incorrect initial
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Date: Sun, 25 Aug 2013 17:49:41 +0300
Organization: Tidorum Ltd
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Date: 2013-08-25T17:49:41+03:00
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On 13-08-25 17:31 , AdaMagica wrote:
> RM 6.4.1(16) A formal parameter of mode in out or out with
> discriminants is constrained if either its nominal subtype or the
> actual parameter is constrained.
> 
> Thus the compiler may assume that variables supplied to calls already
> have the correct subtype.

In other words, as I understand it, this discriminant-check and
Constraint_Error happen when the parameter is passed into the call,
before the assignment statement in the callee.

The discriminant-check occurs because the formal parameter is
constrained to the subtype with a True discriminant. Since the actual
parameter has a False discriminant, the check fails and Constraint_Error
is raised.

Sloppily said: even if the formal parameter mode is "out", if the formal
constrains the discriminants then the discriminants are "in".

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .