Symbol for modifying property lookup?
Jordan Harband
ljharb at gmail.com
Wed Jul 13 20:41:22 UTC 2016
<https://facebook.github.io/react/blog/2016/07/13/mixins-considered-harmful.html>
<https://facebook.github.io/react/blog/2016/07/13/mixins-considered-harmful.html>
https://facebook.github.io/react/blog/2016/07/13/mixins-considered-harmful.html
may also be a helpful read.
(fwiw, any Symbol to modify property lookup would not likely ship before
Proxy was available, so "use Proxy" is a pretty solid suggestion for this)
On Wed, Jul 13, 2016 at 1:04 PM, /#!/JoePea <joe at trusktr.io> wrote:
> Thanks kdex.
>
> In one of my cases, `A` extends `B` extends `C` just so that `A` can have
> characteristics of both `B` and `C`, but it doesn't actually make sense for
> `B` to extend `C` because `B` is not a more specific form of `C` -- `B` and
> `C` are completely unrelated classes; I'm extending `B` from `C` just for
> `A` to have both sets of characteristics.
>
> How might decorators be used instead?
>
> I found some good reading:
>
> -
> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes#Mix-ins
> - http://justinfagnani.com/2015/12/21/real-mixins-with-javascript-classes/
>
> I am currently reading to get ideas on what I might do, but would love
> suggestions if you have any.
>
> */#!/*JoePea
>
> On Wed, Jul 13, 2016 at 3:00 AM, kdex <kdex at kdex.de> wrote:
>
>> Callable class constructors [1] have been discussed at some point.
>> They've been withdrawn [2] in favor of decorators [3], though.
>>
>> [1]
>> https://github.com/tc39/ecma262/blob/master/workingdocs/callconstructor.md
>> [2]
>> https://github.com/tc39/proposals/blob/master/inactive-proposals.md#inactive-proposals
>> [3] https://github.com/wycats/javascript-decorators/blob/master/README.md
>>
>> On Wednesday, July 13, 2016 2:24:10 AM CEST /#!/JoePea wrote:
>> > Oops, I forgot that ES6 classes can't be called using the
>> > `SomeClass.call(...)` form. Is there a workaround for that so that my
>> > constructor can call all of them (besides downgrading to ES5 classes)?
>> >
>> > ```js
>> > class Foo extends new MultiClass(One, Two) {
>> > constructor(...args) {
>> > One.call(this, ...args)
>> > // Error, not allowed
>> >
>> >
>> > Two
>> > .call(this, ...args) //
>> > Error
>> > , not allowed
>> >
>> > }
>> > }
>> > ```
>> >
>> > */#!/*JoePea
>> >
>> > On Wed, Jul 13, 2016 at 1:49 AM, /#!/JoePea <joe at trusktr.io> wrote:
>> >
>> > > Thanks guys, Proxy is the one, but not supported natively enough yet
>> > > unfortunately.
>> > >
>> > > Here is the ES5 solution I came up with, which creates "proxy"
>> methods on
>> > > the "multiPrototype" of the new MultiClass:
>> > >
>> > > ```js
>> > > class MultiClass {
>> > > constructor(...constructors) {
>> > > let constructorName = ''
>> > > let multiPrototype = {}
>> > >
>> > > console.log(' -- Creating new MultiClass.')
>> > >
>> > > for (let i=0, l=constructors.length; i<l; i+=1) {
>> > > const constructor = constructors[i]
>> > >
>> > > constructorName += constructor.name + (i == l-1 ? '' :
>> '+')
>> > > // f.e. SomeClass_OtherClass_FooBar
>> > >
>> > > let props =
>> > >
>> SimplePropertyRetriever.getOwnAndPrototypeEnumerablesAndNonenumerables(constructor.prototype)
>> > > for (let prop of props) {
>> > > multiPrototype[prop] = constructor.prototype[prop]
>> > > console.log(' --- prop', prop)
>> > > }
>> > > }
>> > >
>> > > // temporary object to store the new MultiClass constructor,
>> > > because
>> > > // using an object allows us to programmatically assign a
>> name to
>> > > the
>> > > // function, which we otherwise cannot do without eval().
>> > > let tmp = {
>> > >
>> > > // This new constructor doesn't do much, just has all the
>> given
>> > > // constructor prototypes mixed in to it's own prototype.
>> Be
>> > > sure to
>> > > // call the each constructor manually in the class that
>> > > extends this
>> > > // new MultiClass.
>> > > [constructorName]() {}
>> > >
>> > > }
>> > >
>> > > tmp[constructorName].prototype = multiPrototype
>> > >
>> > > return tmp[constructorName]
>> > > }
>> > > }
>> > > ```
>> > >
>> > > Where `SimplePropertyRetriever` is taken from the MDN article
>> > > [Enumerability and ownership of properties](
>> > >
>> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties#Obtaining_properties_by_enumerabilityownership
>> > > ).
>> > >
>> > > Example usage:
>> > >
>> > > ```js
>> > > class One {
>> > > foo() {console.log('foo')}
>> > > }
>> > >
>> > > class Two {
>> > > constructor() {/* ... */}
>> > > bar() {console.log('bar')}
>> > > }
>> > >
>> > > class Three extends Two {
>> > > constructor(...args) {
>> > > super(...args)
>> > > // ...
>> > > }
>> > > baz() {console.log('baz')}
>> > > }
>> > >
>> > > class FooBar extends new MultiClass(Three, One) {
>> > > constructor(...args) {
>> > > super() // needed, although does nothing.
>> > >
>> > > // call each constructor.
>> > > One.call(this, ...args)
>> > > Three.call(this, ...args)
>> > > }
>> > > oh() {console.log('oh')}
>> > > yeah() {console.log('yeah')}
>> > > }
>> > >
>> > > let f = new FooBar
>> > >
>> > > f.foo()
>> > > f.bar()
>> > > f.baz()
>> > > f.oh()
>> > > f.yeah()
>> > > ```
>> > >
>> > > Any ideas on how else to do it?
>> > >
>> > > */#!/*JoePea
>> > >
>> > > On Tue, Jul 12, 2016 at 1:52 AM, Claude Pache <claude.pache at gmail.com
>> >
>> > > wrote:
>> > >
>> > >>
>> > >> Le 12 juil. 2016 à 02:45, /#!/JoePea <joe at trusktr.io> a écrit :
>> > >>
>> > >> Does one exist? I'm imagining an implementation for
>> > >>
>> > >> ```
>> > >> class Node extends new MultiClass(ImperativeBase, Transformable) {
>> > >> }
>> > >> ```
>> > >>
>> > >>
>> > >> I think that Proxy is the tool for that purpose.
>> > >>
>> > >> How a symbol would work here, since you need a property lookup in
>> order
>> > >> to find that symbol?
>> > >>
>> > >> —Claude
>> > >>
>> > >
>> > >
>> >
>>
>
>
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