Re: types and subtypes

[Jean-Pierre Rosen <rosen@adalog.fr>]

ada_student@yahoo.com a �crit :
> Given,
> 
>               subtype Positive is Integer range 1 .. Integer'Last;
>               type String is (Positive range <>) of Character;
> 
>           the following should be illegal,
> 
>               subtype Count_To_Ten is Integer range 1 .. 10;
>               subtype Ten_Characters is String (Count_to_Ten);
> 
>           and the following should be legal, instead
> 
>               subtype Count_To_Ten is Positive range 1 .. 10;
>               subtype Ten_Characters is String (Count_to_Ten);
> 
> Why is Count_To_Ten allowed to be an Integer even though
> the indices of String are declared as Positives?
> 
Because they are of the same *type*. A subtype does not declare a 
different type, only a restriction (a *constraint*) on the allowed 
values. Since the types are the same, the declaration is OK.

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            J-P. Rosen (rosen@adalog.fr)
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