Promises are inherently eager, but also async - consider that `new Promise(resolve => resolve(1))` is roughly equivalent to `var promise = Promise.resolve(1)`.
My proposal is for a single immediate value, but created on demand (when you call `.get()`) rather than immediately. ----- 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 10:37 AM, Naveen Chawla <[email protected]> wrote: > Could you not do this with a promise? If not, what's missing in promise that > you could do with "lazy"? Sorry if I've missed the whole premise > > On Thu, 31 Aug 2017 at 19:09 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/4c0723bdfa555a1c2cb01341b323c3d4 >>> >>> 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 >> >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
