Re: Why can’t for-of be applied to iterators?

Dmitry Soshnikov dmitry.soshnikov at gmail.com
Tue Jun 11 17:48:59 PDT 2013


On Tue, Jun 11, 2013 at 5:33 PM, Brendan Eich <brendan at mozilla.com> wrote:

> Brian Di Palma wrote:
>
>> Sorry for the OT message.
>>
>> On Tue, Jun 11, 2013 at 6:22 PM, Andrea Giammarchi
>> <andrea.giammarchi at gmail.com>  wrote:
>>
>>> We don't have interfaces ... I know, we could have mixins though,
>>> compatible
>>> with @@things too.
>>>
>>>
>> The concepts of Mixins has cropped up before in discussions and is
>> used in current JS code ( EventEmitter ).
>> I was wondering if it was possible to codify it in ES6 or is there
>> simply no bandwidth/time for that?
>>
>> class MyClass extends MySuper mixin EventEmitter, Iterable {}
>>
> What would this syntax do that couldn't be done better by libraries?
> Remember that extends' RHS is an expression.


Don't wanna go off-topic of course, but: the the fact that RHS is an
expression might you think Object.mixin(...) can be used there:

class Foo extends Object.mixin(...)

The problem with it as I mentioned (and which was successfully and
unfortunately ignored ;)), it accepts only two arguments instead of variant
to mix several objects.

But even it Object.mixin(...) could accept several arguments, we still
can't extend a class with another class _and_ a set of mixins.

class Bar extends Object.mixin(Foo, M1, M2...), where Foo is a class and Ms
are mixin.

To do this you'll need to either express classes's implementation details
(i.e. to break classes abstraction): class Bar extends
Object.mixin(Foo.prototype, M1...);

Or, yeah, to provide a library method:

class Bar extends classWithMixins(Foo, M1, M2...);

(the later example is actually a real implementation we use in local
projects currently).

Another issue with a library method -- it just looks immature for a mature
language. From this viewpoint:

class Bar extends Foo {
  use M1, M2;
}

looks better and mature as all normal OOP langs with mixins/traits. IMHO.

But as long as ES6 spec is already (almost) stable, I agree it can be taken
to something ES7-ish.

Dmitry
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