Re: class-wide objects

[Stephen Leake <Stephen.Leake@gsfc.nasa.gov>]

Matthew Heaney <matthew_heaney@acm.org> writes:

> Then just make it non-primitive:
> 
> generic
>    ...
> package Stacks is
> 
>    type Stack_Type is ...
> ...
>    package Constructors is
> 
>       function  Copy (Stack : Stack_Type) return Stack_Access;
> 
>    end;
> ...
> end Stacks;
> 
> 
> Because Copy is non-primitive, it won't get inherited during derivation.
> 

Another way to make an operation non-primitive is to use 'class:

function Copy (Stack : Stack_Type'class) return Stack_Access;

I've been flip-flopping about which way is "best". Using 'class
sometimes implies re-dispatching in the body, but not always. If the
non-primitive operations belong in a group (like Constructors), then
the local package seems neat. But for other operations, a local
package is just noise, and 'class seems preferable.

-- Stephe