right ... so ... I'm not sure I understand what this proposal would solve. Instead of this: ```js obj.val || (obj.val = getValue()) ```
you want to do this ```js (obj.val || (obj.val = new Lazy(getValue)).get(); ``` Where is the "win" and why is that? On Thu, Aug 31, 2017 at 5:18 PM, Isiah Meadows <[email protected]> wrote: > With my proposed `Lazy` class, if you were to use an instance as a > descriptor, the `this` value it'd receive would not be a `Lazy` > instance like it'd expect. > > Consider it the difference between `a.self` and `b.get()` in your > example. `b.get()` is what I'd be expecting. > ----- > > Isiah Meadows > [email protected] > > Looking for web consulting? Or a new website? > Send me an email and we can get started. > www.isiahmeadows.com > > > On Thu, Aug 31, 2017 at 12:12 PM, Andrea Giammarchi > <[email protected]> wrote: > >> using it in a descriptor would get it passed the wrong `this` > > > > sorry, what? > > > > ```js > > var a = {}; > > var b = {get() { return this; }}; > > Object.defineProperty(a, 'self', b); > > > > a.self === a; // true > > ``` > > > > > > On Thu, Aug 31, 2017 at 5:09 PM, Isiah Meadows <[email protected]> > > wrote: > >> > >> No. `Lazy` is intended to be an object to be used directly, not a > >> descriptor of any kind. > >> > >> (My `lazy.get()` is an unbound method, so using it in a descriptor > >> would get it passed the wrong `this`.) > >> ----- > >> > >> Isiah Meadows > >> [email protected] > >> > >> Looking for web consulting? Or a new website? > >> Send me an email and we can get started. > >> www.isiahmeadows.com > >> > >> > >> On Thu, Aug 31, 2017 at 9:39 AM, Andrea Giammarchi > >> <[email protected]> wrote: > >> > the following is how I usually consider lazy values > >> > > >> > ```js > >> > class Any { > >> > _lazy(name) { > >> > switch (name) { > >> > case 'uid': return Math.random(); > >> > // others ... eventually > >> > } > >> > } > >> > get uid() { > >> > var value = this._lazy('uid'); > >> > // from now on, direct access > >> > Object.defineProperty(this, 'uid', {value}); > >> > return value; > >> > } > >> > } > >> > > >> > const a = new Any; > >> > a.uid === a.uid; // true > >> > ``` > >> > > >> > If I understand correctly your proposal is to use Lazy as generic > >> > descriptor, is that correct ? > >> > > >> > ```js > >> > Object.defineProperty({}, 'something', new Lazy(function (val) { > >> > return this.shakaLaka ? val : 'no shakaLaka'; > >> > })); > >> > ``` > >> > > >> > ??? > >> > > >> > If that's the case I see already people confused by arrow function > >> > in case they need to access the context, > >> > plus no property access optimization once resolved. > >> > > >> > It's also not clear if such property can be set again later on (right > >> > now it > >> > cannot) > >> > 'cause lazy definition doesn't always necessarily mean inability to > >> > reassign. > >> > > >> > What am I missing/misunderstanding? > >> > > >> > Regards > >> > > >> > > >> > > >> > On Thu, Aug 31, 2017 at 2:21 PM, Isiah Meadows < > [email protected]> > >> > wrote: > >> >> > >> >> It'd be really nice if lazy values made it into the spec somehow. > I've > >> >> already found myself using things like this [1] quite a bit, and I've > >> >> also found myself frequently initializing properties not on first > >> >> access. > >> >> > >> >> [1]: > >> >> https://gist.github.com/isiahmeadows/4c0723bdfa555a1c2cb01341b323c3 > d4 > >> >> > >> >> As for what would be a nice API, maybe something like one of these? > >> >> > >> >> ```js > >> >> class Lazy<T> { > >> >> constructor(init: () => T); > >> >> get(): T; // or error thrown > >> >> } > >> >> > >> >> function lazy<T>(init: () => T): () => T; // or error thrown > >> >> > >> >> function lazy<T>(init: () => T): { > >> >> get(): T; // or error thrown > >> >> } > >> >> ``` > >> >> > >> >> Alternatively, syntax might work, with `do` expression semantics: > >> >> > >> >> ```js > >> >> const x = lazy do { ... } > >> >> // expose via `x.get()` or just `x()` > >> >> ``` > >> >> > >> >> ----- > >> >> > >> >> Isiah Meadows > >> >> [email protected] > >> >> > >> >> Looking for web consulting? Or a new website? > >> >> Send me an email and we can get started. > >> >> www.isiahmeadows.com > >> >> _______________________________________________ > >> >> es-discuss mailing list > >> >> [email protected] > >> >> https://mail.mozilla.org/listinfo/es-discuss > >> > > >> > > > > > >
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