Re: [gobo-eiffel-develop] check if ET_CLASS_TYPE can be used as actual parameter

[Thomas D. <th...@de...>]

Thanks a lot! (again).

Kind Regards

Thomas

On 7/19/07, Eric Bezault <er...@go...> wrote:
> Thomas Delaet wrote:
> > Hi,
> >
> > I have two ET_CLASS objects: a and b.
> > Assume that the first object (A) has one generic parameter. If that
> > parameter is constrainted, I want to check if another object (B)
> > conforms to the generic constraint.
> >
> > Based on my current knowledge, I guess I should use the
> > conforms_to_type feature of ET_CLASS, but I don't know how to use this
> > feature correctly in this case.
> >
> > The signature of conforms_to_type is:
> >
> > conforms_to_type (other: ET_TYPE; other_context: ET_TYPE_CONTEXT;
> > a_context: ET_TYPE_CONTEXT; a_universe: ET_UNIVERSE): BOOLEAN
> >
> > So, I guess I should call this feature on object a.
>
> You meant object b, not a.
>
> > The question is
> > then: what values do I have to fill in for the other arguments, except
> > for a_universe?
> >
> > It think the value of other should be
> > a.formal_parameters.item(1).constraint, so that leaves other_context
> > and a_context to be filled in ...
>
> The context is where your type comes from. For example the type
> 'like Current' has different meanings depending on whether it
> appears in class STRING or in class ARRAY. If the context is
> class STRING, then we can say that 'like Current' conforms to
> COMPARABLE, which is not the case if the context was ARRAY.
> Furthermore, in the context of 'LINKED_LIST [STRING]' type G
> conforms to STRING.
>
> So if your types appears in class C, for example:
>
> class A [G -> LIST [H], H] ...
> class B inherit LINKED_LIST [STRING] ...
>
> class C
> feature
>      a: A [B, COMPARABLE]
>
> what we need to prove is that in the context of C
> the type B conforms LIST [H] in the context of
> A [B, COMPARABLE]. Which is indeed the case because
> B in the context of C is B itself, and 'LIST [H]'
> in the context of A [B, COMPARABLE] is nothing else
> but LIST [COMPARABLE], and B conforms to LIST [COMPARABLE].
>
> As an example, have a look at ET_TYPE_CHECKER.check_class_type_validity.
>
> --
> Eric Bezault
> mailto:er...@go...
> http://www.gobosoft.com
>


-- 
Thomas