Re: Using the GNAT defined attribute: 'Enum_Rep

["W. Wesley Groleau x4923" <wwgrol@pseserv3.fw.hac.com>]

>     Here's a little problem which I could use some help handling:
> 
>     .... to create an integer type that is the
>     same size as the enumerated type. Here's a code fragment:
> 
>     type Temp_Integer is range Integer'First..Integer'Last ;
>     for Temp_Integer'Size use User_Types.CL_Evt_Status'Size ;
>                             --^^^^^^^^^^^^^^^^^^^^^^ The enumerated type.
> 
>     .... new  Ada.Unchecked_Conversion (
>             Source  => Temp_Integer ;
>             Target  => User_Types.CL_Evt_Status) ;

you've probably already discovered that Integer'First..Integer'Last
forces a minimum on Temp_Integer'Size.  And in Ada 83, the above 
would not be legal because 'Size is _defined_ as non-static, thus 
can't be used to specify another 'Size.  To get around this, I did

    CL_Evt_Status_Size : constant := ######;
    for CL_Evt_Status'Size use CL_Evt_Status_Size;

Now CL_Evt_Status_Size can be used anywhere that CL_Evt_Status'Size
can be used, and it will be static.

>      'Pos and 'Val. ... will work If and only if the representation is
>     identical to the position numbers - what you get if you don't
>     specify a representation. ....

Is this true ?  Seems to me it's legal (though I've never seen
it happen) for an implementation to generate anything it wanted
for a representation as long as ordering, indexing, etc. worked.

I can imagine a CPU where a bit per value is more efficient, i.e., 
an implicit

   for Enum use ( 0, 1, 2, 4, 8, 16, 32, ... );

though, again, I've never seen that done.

-- 
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    Wes Groleau, Hughes Defense Communications, Fort Wayne, IN USA
Senior Software Engineer - AFATDS                  Tool-smith Wanna-be
                    wwgrol AT pseserv3.fw.hac.com

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