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From: Christoph Grein <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: Confused about Attribute Size?
Date: Tue, 22 Jan 2002 09:00:43 +0100 (MET)
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Date: 2002-01-22T09:00:43+01:00

> 
> type My_Type is
>     (startbit,
>      endbit,
>      timeout,
>      spare,
>      nextbit,
>      ......
>      ......
>      lastbit);

This assigns _values_ (not bit positions) to the enumeration literals that shall 
be used to represent them internally, i.e. startbit has the value (or is another 
name for) 0, lastbit the value 15. However you have no access to the internal 
values (you can't add them e.g. startbit + timeout is illegal).

> for My_Type use
>     (startbit =>0,
>      endbit=>1,
>      timeout=>2,
>      spare=>3,
>      nextbit=>4,
>      ......
>      ......
>      lastbit=>15);
> 
> for My_Type'Size use 8;

Since a value of 15 = 2#00001111# can be represented in 8 bits, there is no 
problem.

> type My_Type_Array is array (My_Type) of Boolean;
> 
> What I don't understand is how you can assign the size to 8 bits? How will
> this work when
> there are 16 bits in the type? What will be the size of the array?
> This example was in Ada 83 could this be a clue?

In Ada95, there is no need to explicitly define this default representation, see 
RM 13.4(8).