Re: Container reqs

[Ted Dennison<dennison@telepath.com>]

In article <3BCEF4B8.B1AC6965@brighton.ac.uk>, John English says...
>
>I do something like this in JEWL. There's a reference-counted tagged
>type in package JEWL (non-generic parent):
>
>  type Reference_Counted_Type is tagged limited
>    record
>      Count : Natural := 1;
>    end record;
>
>  procedure Cleanup (Object : in out Reference_Counted_Type);
>
>  type Reference_Counted_Ptr is access all Reference_Counted_Type'Class;
>
>  type Controlled_Type is new Ada.Finalization.Controlled with
>    record
>      Pointer : Reference_Counted_Ptr;
>    end record;
>
>  procedure Finalize (Object : in out Controlled_Type);
>  procedure Adjust   (Object : in out Controlled_Type);
>
>and then JEWL.Windows (which is generic) uses this Controlled_Type as
>a component (actually *the* component) in all the window types, so that
>all windows are implemented as pointers to reference-counted types.
>The actual object that a particular type of window points to is one
>of a variety of possible derivations which are defined in a private
>child and produced by constructor (factory) functions.

I still don't see how that allows you to declare something in the generic that
can be managed by the controlled object. You can manage the
"reference_counted_type", but if I declare some new type that needs to be
managed in my generic, the only way to get Controlled_Type to manage it is to
derive it from "reference_counted_type". If I do that, I'm back to the situation
where my generic can only be instantiated at the library level.

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

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