Re: Ada.Locales pseudo-string types

[Adam Beneschan <adam@irvine.com>]

On Tuesday, August 7, 2012 6:14:13 AM UTC-7, Marius Amado-Alves wrote:
> I took the chance to learn subtype aspect clauses, and changed Ada_Locales thus:

> 
>    subtype Country_Code is String (1 .. 2) 
>       with Static_Predicate =>
>          Country_Code (1) in 'A' .. 'Z' and
>          Country_Code (2) in 'A' .. 'Z';
> 
> (Now Text_IO.Put works of course, but I think it should work in the first place.)

If GNAT accepts this, then *that* is a compiler bug, I think.  I don't see how this expression is allowed as a static predicate.  (The rule in 3.2.4(17) says that the "current instance" may be used as the expression in a membership test.  But it looks to me that "current instance" refers strictly to the name Country_Code, period, without any indexes or component selectors or anything.  So you can't use Country_Code(1) in a static predicate, as I interpret it.)  Dynamic_Predicate might work.  I haven't studied all the rules, though.


> This little experiment exposed other strange things:
>
> (1) It seems the compiler accepts the type name, in the aspect clause, as a representative of a value of the type. I could not find this documented in the RM.

That's what "current instance" means.  See 8.6(17).

> 
> (2) The aspect clause does not seem to have effect. The following code compiles and runs normally.
> 
>    CC : Ada_Locales.Country_Code := "34";
> 
> Of course (2) can be an effect of the semantic void of (1).

                              -- Adam