Re: class wide object in generic package

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

Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov> writes:

> "Ehud Lamm" <mslamm@huji.ac.il> writes:
> 
> > It seems to me you want as a generic paramter any type that has the Eval
> > operation.
> > So you can define a parent type having this operation (say an abstract type
> > called Evalable).
> > Now you can define the generic
> > 
> > with Evalable_Pak;
> > generic
> >     type My_Evalable is new Evalable_Pak.Evalable with private;
> > ....
> > 
> > My_Evalable will have a primitive Eval operation.
> 
> Yes, it will have an Eval operation, but that operation will _not_ be
> visible in the generic body.

That's not correct.  My_Evaluable inherits a primitive Eval from
Evalable_Pak.Evalable, and this may be called in the generic body.
In the instance, it will call the Eval for the actual type.

>... The generic body does _not_ "read" the
> package spec for Evalable_Pak. 

It does.

> That's why you need the generic formal package parameter; then the
> generic body _does_ see everything in the generic formal package spec.

That's another way of doing things.

- Bob