P T Withington
ptw at pobox.com
Mon Jan 18 13:05:40 PST 2010
On 2010-01-18, at 15:41, Mark S. Miller wrote:
> On Mon, Jan 18, 2010 at 7:32 AM, P T Withington <ptw at pobox.com> wrote:
>> In the various classes-as-sugar proposals, is there a way to test if one
>> class is a subclass of another? Is it as simple as:
>> classa.prototype instanceof classb
>> In some of them, yes. For the desugaring presented at <
> WobblyPoint.prototype instanceof Point
> would work for the right reason.
Yeah, I saw (and liked) that.
In OpenLaszlo we allow mixins (which are flattened into a single-inheritance prototype chain + multiple-inheritance interfaces), and we adopted the AS3 `is` operator, so we say:
subclass.prototype is superclass
and superclass can be either a class or a mixin. [Sadly this doesn't work in AS3!]
> In some later proposals, no, because the
> concept of subclassing is being replaced by the concept of trait
> combination. Since this gives non-tree-like subtype relationships, it can't
> accommodate instanceof.
>> Should there be a `subclassof` operator?
Do you have a pointer to the later proposals?
I guess my question stands. Even if I implement classes using traits, I would want to be able to ask if a class had a particular trait. I guess that would have to be part of the class protocol then, not a language primitive.
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