Overriding Map/etc with get/set hooks?

Mark S. Miller erights at google.com
Mon Aug 11 18:48:36 PDT 2014

On Mon, Aug 11, 2014 at 6:33 PM, Domenic Denicola <
domenic at domenicdenicola.com> wrote:

> When I last looked at this, it seemed like a perfect use case for [Traits](
> http://soft.vub.ac.be/~tvcutsem/traitsjs/tutorial.html). A "Set-like"
> trait would require definitions for add, delete, and [Symbol.iterator], but
> provide has, forEach, entries, keys, values, clear, and size, plus any
> future interfaces.
> Then you would implement such set-likes by mixing in the set-like trait
> into your prototype, which contains type-restricted definitions for add,
> delete, and [Symbol.iterator] (plus probably some of the other methods for
> performance reasons).
> Presumably a future version of ES that contains traits would define
> set-like, map-like, and other traits that could be used.

Hopefully. But any future JS traits system should somehow play well with JS
classes. The semantics of classes we accepted into ES6 makes that difficult
but probably not impossible.

Just for the record: Some of the rejected class proposals were designed to
play well with future traits systems. In the end I agree with the
pragmatics that caused these to be rejected in favor of the current one.
But we paid the costs of making traits harder and more awkward, to the
point that we may never have one we deem acceptable. We'll see.

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