Re: [boost] [review] Review of Flyweight library started January 21and still running!: equality semantic

From: vicente.botet (vicente.botet_at_[hidden])
Date: 2008-01-27 16:16:58

Thanks Joaquin for your response.

JOAQUIN LOPEZ MUÑOZ wrote
> Umm, this approach is interesting! Better yet, instead of relying on an
> explicit are_equals function, we can just require that
> Factory::handle_type is EqualityComparable and use that:
>
>   friend bool operator==(const flyweight& x,const flyweight& y)
>   {
>     return x.h==y.h;
>   }
>
> As a matter of fact, all the current factories have EqualityComparable
> handles that precisely implement reference equality semantics, so
> it looks all very natural. This approach would solve the second
> problem of the list I presented at the review notes:
>
>  * The resulting equality semantics might not coincide with that of
>   the underlying T; the possibility of this hapenning and making a
>   real difference is probably small, though.
>  * The assumption that equal flyweight objects always share their value
>   interfere with potential extensions to the library, like the
>   no-factory proposal by Throsten Ottosen.
>

This seams OK to me, finally it will be the responsability  of the factory 
to define the equality operator
for its handle_type.

> but would not address the first point.

I think that I don't really understant the first problem:
if we have T t1, t2 such t1==T2 it may happens that
handle_type of t1 != handle_type of t2

Please could you give us un example on which the first problem is present?

Regards

---------------------------
Vicente Juan Botet Escriba