Re: generics with multiple constraints

On Fri, 01 Sep 2006 00:00:17 +0200, Felix Breuer <felix@[EMAIL PROTECTED]
> wrote:
> suppose I want to create a generic class
>
>   A [B -> COMPARABLE  & HASHABLE]
>
> meaning that I want classes B that can act as a parameter to A
> to descend from both COMPARABLE and HASHABLE. How can I
> achieve this? Eiffel's syntax seems to allow only one constraint per
> formal parameter. Is there some workaround? This looks like a fairly
> standard situation to me, so maybe someone encountered this
> before?
>
> Thanks,
> Felix

This is currently not possible and also conceptually not as easy as it  
seems: what is the static type of a variable declared 'b : B'? What are  
the features that can be called on it?

A workaround might be to declare 'A[B->COMPARABLE]' and to use assertions 

for the conform type checks for HASHABLE. Not nice, no static typing ...

Bernd

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