On 7/27/05, Larry Wall <[EMAIL PROTECTED]> wrote: > On Wed, Jul 27, 2005 at 11:00:20AM +0000, Luke Palmer wrote: >> Everything that is a Num is a Complex right? > > Not according to Liskov. Num is behaving more like a constrained > subtype of Complex as soon as you admit that "isa" is about both > implementation and interface. By the interface definition it's > slightly truer to say that Complex is a Num because it extends Num's > interface. But this is one of the standard OO paradoxes, and we're > hoping roles are the way out of it.
Well, everything that is a Num is a Complex in a value-typed world, which Num and Complex are in. I don't like reference types much (though I do admit they are necessary in a language like Perl), and I'm not sure how this fits there anymore. Anyway, that's beside the point, since a supertyping need is still there for referential types. Luke
