Minimalist (why) classes ?

John J Barton johnjbarton at johnjbarton.com
Sun Nov 13 11:50:40 PST 2011


On Sun, Nov 13, 2011 at 2:36 AM, Axel Rauschmayer <axel at rauschma.de> wrote:
> It depends on what kind of `extends` you mean:
> - Inheritance: Even though data being kept in prototypes is rare, it’s
> usually better to chain prototypes even when ignoring aliasing problems (no
> redundant properties, instanceof works transitively). Performance
> degradation should be negligible due to internal optimizations.
> - Merging objects: Shallow copy is the way to go.

Perhaps you mean: 'it depends on the use of the object returned by
|extends()|'. But I don't understand your categories. Mine:

Object-like: you want to use the returned object directly. I think a
dev imagines extend() as a kind of initialization, a merger operation:
   var a = merge(b,c,d);
In this case you do not expect deep copy, you expect shallow,
reference copy. If I change d.color, I expect that a.color is changed.
 Or rather, I would say that a dev would not be surprised at this
behavior.

Class-like: you want to use the returned object indirectly, to create
other objects via Foo.prototype/new Foo or similar operation.  Here we
are operating on two levels. In the abstract level we are combining
objects to define factory; in the concrete level we are creating
objects based on that factory.  The data on the inputs to the abstract
level are -- at most -- relevant as initial values for the concrete
level.   You want something like deep copy.

As I mentioned elsewhere, the Object-like merge can be used (with
care) on collections of methods then applied to Foo.prototype. That's
how we get along now: one operation covers both cases just not always
robustly.

jjb


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