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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Subject: Re: Run-Time Type Assignment
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Date: Wed, 28 Aug 2002 13:41:07 GMT
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Date: 2002-08-28T13:41:07+00:00
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"Robert C. Leif" <rleif@rleif.com> writes:

> --Variant Record Approach
> --Does not work
>    type Parameter_Rec_Psuedo_Tagged_Type (Num_Parameters :
> Num_Parameters_Type) is --range 1..2
>    record
>       case Num_Parameters  is
>          when 1 =>
>             Parameter_1: Parameter_1_Type;
>          when 2 =>
>             Parameter_1: Parameter_1_Type;
>  		--Parameter_1 conflicts with declaration 2 lines above.

So change the name.  Or combine into one field outside the variant part,
as suggested in another note.

Same-named record fields are illegal in Pascal, too, by the way.

> -- tagged record
> package Array_Of_Records_Class_Pkg is new Array_Of_Records_G_Pkg(
>    Length      => Num_Of_Records,   
>    Record_Type => Record_Type'Class); 
> --Bombs because "Actual for "Record_Type" must be a definitive subtype"
> --How can I make this dispatch based the Num_Parameters?

You don't show the generic, so I can't tell what you're trying to do,
but Record_Type has to have (<>) discriminants to allow an indefinite
actual.  (Roughly speaking, "indefinite" means that different objects of
the subtype will have different sizes -- which is true of T'Class.)

If your goal is to have an array of different-sized components,
that's not directly allowed in Ada.  You need some form of indirection,
or some such thing.

If you change the variant record above to have a defaulted discriminant,
then you can create an array of them, but they will be allocated the max
size in most compilers.

- Bob