Re: How to write TYPECASE in Ada 95?

[tmoran@bix.com (Tom Moran)]

>If you want to extend a type with arbitrary behavior, you could take a
>look at using the Visitor pattern.  Ada implementations of this pattern
>are available at the ACM patterns archive.

><http://www.acm.org/archives/patterns.html>
Am I looking at the right place?  I see

>package body Equipment.Pricing is


>   function Get_Total_Price
>     (Equipment : Root_Equipment'Class) return Dollars is
>   begin
>      if Equipment in Floppy_Disk then

>         declare
>            Disk : Floppy_Disk renames Floppy_Disk (Equipment);
>         begin
>            return Get_Price_Of_Floppy_Disk (Disk);
>         end;

>      elsif Equipment in Hard_Disk then

>         declare
>            Disk : Hard_Disk renames Hard_Disk (Equipment);
>         begin
>            return Get_Price_Of_Hard_Disk (Disk);
>         end;
which surely looks pretty similar to

> procedure Serve_Fruit(Dish : in Fruit'class) is
>  begin
>    if Dish in Apple'class then Serve(Apple(Dish));
>    ...
>    elsif Dish in Watermelon'class then Serve(Watermelon(Dish));