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From: Mats Weber <Mats.Weber@elca-matrix.ch>
Subject: Re: Question about base types
Date: 1997/01/27
Message-ID: <32ECD6B6.3B5A@elca-matrix.ch>#1/1
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Date: 1997-01-27T00:00:00+00:00
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> I have a question about the relationship between types, first named
> subtypes, and base types.
> 
> If I declare an integer type, say
> 
> type T is range 1 .. 10;
> 
> Then I think that according to the Ada model this means I'm declaring some
> unnamed type, but whose first named subtype is T:
> 
> type <anonomous parent of T> is System.Min_Int .. System.Max_Int;
> subtype T is <anonomous parent of T> range 1 .. 10;
> 
> Do I have this correct?

No, but almost. the first line is wrong and should read

type <anonomous parent of T> is range <min> .. <max>;

where <min> and <max> are anonymous static implementation defined
constants that depend on the range you give in your type declaration.
For 1 .. 10, the compiler is quite likely to choose <min> = -128 and
<max> = 127 in order to store your type in a single byte.

> Now what is the relationship of T'Base to this model?  Is T'Base the name
> of the anonomous parent type

Yes

> type T'Base is System.Min_Int .. System.Max_Int;
> subtype T is T'Base range 1 ..  10;
> 
> Did the "anonmous parent" go away in Ada 95?  Or is it still

The mechanism has changed a little, but the effect remains basically the
same.

> I can declare objects of type T'Base, right?

You can in Ada 95, but not in Ada 83.

> O : T'Base;
> 
> Is this declaration the same as
> 
> O : <anonomous parent of T>;
> 
> Enquiring minds want to know...

This cannot be answered because the second declaration is illegal :-).