Re: Run-Time Type Assignment

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Robert C. Leif" <rleif@rleif.com> writes:

> From: Bob Leif
> From: Bob Leif
> To: Fellow Readers of Comp.Lang.Ada
> Firstly, thanks to all who suggested implementations. I now have a
> solution based on the Example from Norman Cohen's Ada as a second
> language page 377.
> The two pages and main procedure below compile. Unfortunately, type
> Para_Rec_Psuedo_Tagged_Type is brute force approach. Does anyone have a
> simpler implementation?

In this case, all the "Para"'s are of type Positive, so you could make
an array inside the record, bounds 1..Num_Paras.  You lose some range
checking, unfortunately.  If the types were not all the same type, then
*make* them be all of the same type by the usual methods (pointer to
class-wide, pointer to variant record, etc).

> ------------------------------------------------------
> package Parameter_Recs_Pkg is
>    subtype Para_1_Type is Positive range 1..64_000;
>    subtype Para_2_Type is Positive range 1..256;
>    subtype Para_3_Type is Positive range 1..1024;
>    subtype Para_4_Type is Positive range 1..2048;
>    subtype Para_5_Type is Positive range 1..4096;
> 
>    subtype Num_Paras_Type is Positive range 1..5;
>    Num_Paras : Num_Paras_Type := 1;  
> 
>    type Para_Rec_Psuedo_Tagged_Type (Num_Paras :Num_Paras_Type) is
>    record
>       Para_1  : Para_1_Type; --Always has one parameter
>       case Num_Paras  is
>          when 1 =>
>             null;
>          when 2|3|4|5 =>
>             Para_2  : Para_2_Type;
>             case Num_Paras  is
>                when 1|2 =>
>                   null;
>                when 3|4|5 =>
>                   Para_3  : Para_3_Type;
>                   case Num_Paras  is
>                      when 1|2|3 =>
>                         null;
>                      when 4|5 =>
>                         Para_4  : Para_4_Type;
>                         case Num_Paras  is
>                            when 1|2|3|4 =>
>                               null;
>                            when  5 =>
>                               Para_5: Para_5_Type;
>                         end case;
>                   end case;
>             end case;
>       end case;
>    end record;
> end Parameter_Recs_Pkg;

- Bob