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From: Christoph Grein <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: constrained subtypes
Date: Wed, 13 Mar 2002 07:22:09 +0100 (MET)
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Date: 2002-03-13T07:22:09+01:00

> From: Jeffrey Carter <jeffrey.carter@boeing.com>

> With parentheses, you have an expression, which is of the unconstrained
> base subtype (Integer'Base), not the constrained subtype. Expressions
> are always evaluated using the unconstrained base type. This allows
> things such as
> 
> subtype X is Integer range 1 .. 8;
> Y : Integer := 16;
> Z : X;
> ...
> Z := Y / 2;
> Y := 3 * Z;
> 
> to be legal. "Y / 2" is not necessarily in X, so a constraint check is
> performed before assignment. "3 * Z" is not of subtype X, but is legal,
> even though Z is of subtype X, because it is an expression.
> 
> This is why "case Z" and "case (Z)" are different. "Case Y" and "case
> (Y)" cover the same range, so you don't see a difference (though it's
> there).
> 

Nice exegesis, I also thought it was this way. But when I looked into the RM, I 
found only:

4.4(7) primary ::= numeric_literal | null | string_literal | aggregate
                 | name | qualified_expression | allocator | (expression) 

4.4(9) Each expression has a type; it specifies the computation or retrieval
       of a value of that type. 

4.4(10) The value of a primary that is a name denoting an object is the
        value of the object. 

Thus (X) has to be further reduced to X, and then X denotes an object,
so where is the difference between "case X is" and "case (X) is"?

I would like to see a formal exegesis with the RM.