Re: (no subject)

[dweller@dfw.net (David Weller)]

In article <4ke8pk$bua@post.tau.ac.il> you write:
>I would Like to write an abstract package that will implement Sets in
>two ways, one with list and one with array, I need to declare a base 

This is very similar to how the Booch Components does it...

>type and then derive from it. doe's anybody has something like it 
>or can help me write it.(I don't know how to write the spec for the
>the derived type)
>
>package Sets is 
>
>generic
>   type Set_Element is private;
>
>package Abstract_Sets is
>  
>   type Set is abstract tagged private;
>
> ..[various functions deleted]
>
>private
>   type Set is abstract tagged null record;
>end Abstract_Sets;
>

I think you want:

generic
   type Set_Element is private;  -- or (<>), depending on your preferences
package Sets is
	type Set is abstract tagged private;

	[same functions that you already had...]

private
	type Set is abstract tagged with null record;
end Sets;

then...

generic	-- must have "generic" since parent is a generic
package Sets.List_Based is

	type List_Set is new Set with private;

	[redefinitions of abstract operations]
private
	type List_Set is new Set with record...
end Sets.List_Based;

Similarly for Sets.Array_Based  (or whatever you call them)