On 03.10.2010 1:06, Brendan Eich wrote:
On Sep 6, 2010, at 7:17 AM, Dmitry A. Soshnikov wrote:
On 02.10.2010 17:29, Brendan Eich wrote:
On Sep 6, 2010, at 1:43 AM, Dmitry A. Soshnikov wrote:
For what to create a proxy? It's only for catch-traps (yes, it may be used additionally
to create a _catcher_ with "Array" [[Class]], but without additions -- i.e. if
a user wants just to inherit from Array.prototype and to have all arrays' stuff --
proxies are not needed to him).
Proxies are required to update length to be one greater than index (property
name-string P such that ToString(ToUint32(P)) == P and ToUint32(P) is not 2^32
- 1) when setting an indexed property. Array's magic [[Put]] is not inherited.
Yep, true, but if we have ability to specify the [[Class]] -- we'll have
overloaded [[DefineOwnProperty] (or [[Put]] in ES3).
Here's this ad-hoc (with using __proto__ injection) implementation:
http://gist.github.com/607668
By the way, at first glance, the ability to specify [[Class]] with using first
level of inheritance is not so convenient and needed.
Indeed. Also, I would not say this shows the abilitiy to specify [[Class]] as if that
internal property could be specified as "Array" for a non-Array instance -- all
you are doing is making an Array instance whose [[Prototype]] links to a user-specified
object.
Yeah, of course, but it's just a shim with resources I have (JS) :) At
lower level of implementation, I'd operate with different approach.
That's novel in ES5, i.e., without settable __proto__ and without Array.create
as Jorge pointed out.
Yes, but Array.create should do the same. Implementation is abstract and
isn't essential. The end result is essential. With the same end result
all implementation fit (if to consider only the semantics of course).
/be
Because with the same success we may create a simple array and augment it with
needed properties. However, starting from the second and later inheritance
levels -- it may be convenient.
This is if to talk about prototypal inheritance. If to consider class-based
inheritance (that is, with using constructors), possibly it can be sense in the
special meta-constructor (a constructor of constructors) which may specify,
objects of what kind (of what [[Class]]) a newly created constructor may
produce.
P.S.: in addition, the Proxy constructor may also accept className parameter. But repeat -- proxies
are needed to trap the property access. If a user just want to have Array.prototype in inheritance
chain and at the same time have an object of the "Array" kind, he just creates it with
specifying this kind. He don't need to write a proxy's handler for that. Howerver, if he does need
the catcher -- he creates a proxy of "Array" kind.
Dmitry.
/be
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