so in JavaScript that results into this._db() each time, resolved lazily
with the first value returned once ?
I still think my approach is cleaner and more transparent.
`get _thing() { return defineProperty(this, 'thing', value) }`
but if your TS-ish stuff translates into that, works for me
On Thu, Aug 31, 2017 at 8:49 PM, Isiah Meadows <isiahmead...@gmail.com>
wrote:
> It takes a function, and returns a function that (if necessary)
> initializes the value and then gets it.
> -----
>
> Isiah Meadows
> m...@isiahmeadows.com
>
> 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 3:43 PM, Andrea Giammarchi
> <andrea.giammar...@gmail.com> wrote:
> > Sorry I don't speak TS, I speak ES.
> >
> > Can you please tell me in JavaScript what does that do?
> >
> > On Thu, Aug 31, 2017 at 8:18 PM, Isiah Meadows <isiahmead...@gmail.com>
> > wrote:
> >>
> >> Note the TS-ish declaration above it. That's the variant I was
> >> referring to (I presented about 3 different variants initially).
> >>
> >> ```ts
> >> // The declaration I included
> >> declare function lazy<T>(init: () => T): () => T;
> >> ```
> >>
> >>
> >> On Thu, Aug 31, 2017 at 3:05 PM, Andrea Giammarchi
> >> <andrea.giammar...@gmail.com> wrote:
> >> > it wouldn't work, would it ? I mean, you still have to pass through
> the
> >> > "ugly" _db.get() thingy, right?
> >> >
> >> > how do you access and trigger the lazy bit within the class?
> >> >
> >> > On Thu, Aug 31, 2017 at 7:56 PM, Isiah Meadows <
> isiahmead...@gmail.com>
> >> > wrote:
> >> >>
> >> >> What about this (using the stage 3 class fields proposal)?
> >> >>
> >> >> ```js
> >> >> declare function lazy<T>(init: () => T): () => T;
> >> >>
> >> >> class WithLazyVals {
> >> >> _db = lazy(() => new Promise(...));
> >> >> }
> >> >> ```
> >> >> -----
> >> >>
> >> >> Isiah Meadows
> >> >> m...@isiahmeadows.com
> >> >>
> >> >> 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 1:34 PM, Andrea Giammarchi
> >> >> <andrea.giammar...@gmail.com> wrote:
> >> >> >> this proposal doesn't compose well with classes
> >> >> >
> >> >> > to expand a little, if you were proposing
> >> >> >
> >> >> > ```js
> >> >> > class WithLazyVals {
> >> >> > lazy _db() { return new Promise(...); }
> >> >> > }
> >> >> > ```
> >> >> >
> >> >> > I would've taken first flight to come over and hug you.
> >> >> >
> >> >> > Best Regards
> >> >> >
> >> >> >
> >> >> >
> >> >> >
> >> >> > On Thu, Aug 31, 2017 at 6:25 PM, Andrea Giammarchi
> >> >> > <andrea.giammar...@gmail.com> wrote:
> >> >> >>
> >> >> >> > How often do you start out with a class like this ...
> >> >> >>
> >> >> >> Never, like I've said. This is the lazy pattern I know since ever.
> >> >> >>
> >> >> >> ```js
> >> >> >> class Foo {
> >> >> >> get _db() {
> >> >> >> return Object.defineProperty(this, '_db', {
> >> >> >> value: new Promise((resolve, reject) => {
> >> >> >> // open a database connection
> >> >> >> // set up whatever tables you need to
> >> >> >> // etc.
> >> >> >> })
> >> >> >> })._db;
> >> >> >> }
> >> >> >> }
> >> >> >> ```
> >> >> >>
> >> >> >> Whenever you need, you just access `this._db`, no need to create
> an
> >> >> >> enumerable variable and a class method.
> >> >> >>
> >> >> >> It looks cleaner to me.
> >> >> >>
> >> >> >>
> >> >> >> > Things you don't want to initialize right away because
> >> >> >> > initialization
> >> >> >>
> >> >> >> You don't really have to convince me, I've written lazy properties
> >> >> >> since
> >> >> >> getters and setters were introduced [1]
> >> >> >>
> >> >> >> All I am saying is that this proposal doesn't compose well with
> >> >> >> classes,
> >> >> >> it's just yet another SuperPrimitive for the language.
> >> >> >>
> >> >> >> It is also something trivial to implement on user land, yet I
> >> >> >> haven't
> >> >> >> seen
> >> >> >> many writing code like the following:
> >> >> >>
> >> >> >> ```js
> >> >> >> function Lazy(fn) {
> >> >> >> let c = false, v;
> >> >> >> return {get(){ return c ? v : (c = !c, v = fn()) }};
> >> >> >> }
> >> >> >>
> >> >> >> var o = Lazy(() => Math.random());
> >> >> >> o.get(); // ...
> >> >> >> ```
> >> >> >>
> >> >> >> Maybe it's me that hasn't seen this widely adopted from some
> >> >> >> library?
> >> >> >>
> >> >> >> Anyway, this is just my opinion, maybe others would be happy with
> >> >> >> this.
> >> >> >>
> >> >> >> Best Regards
> >> >> >>
> >> >> >> [1] Class.lazy example
> >> >> >>
> >> >> >>
> >> >> >> https://github.com/WebReflection/prototypal/blob/master/Class.md#
> classlazycallback
> >> >> >>
> >> >> >>
> >> >> >>
> >> >> >> On Thu, Aug 31, 2017 at 6:03 PM, Isiah Meadows
> >> >> >> <isiahmead...@gmail.com>
> >> >> >> wrote:
> >> >> >>>
> >> >> >>> It'd solve a problem similarly to Kotlin's `by lazy { ... }`
> >> >> >>> delegate,
> >> >> >>> .NET's `System.Lazy<T>`, Swift's `lazy var`, among many other
> >> >> >>> languages. It's very useful for lazy initialization [1], such as
> >> >> >>> lazily setting up a database, requesting a resource, among other
> >> >> >>> costly things. [2]
> >> >> >>>
> >> >> >>> How often do you start out with a class like this, where you have
> >> >> >>> an
> >> >> >>> expensive resource you don't want to open right away?
> >> >> >>>
> >> >> >>> ```js
> >> >> >>> class Foo {
> >> >> >>> constructor() {
> >> >> >>> this._db = undefined
> >> >> >>> }
> >> >> >>>
> >> >> >>> _initDb() {
> >> >> >>> if (this._db) return this._db
> >> >> >>> return this._db = new Promise((resolve, reject) => {
> >> >> >>> // open a database connection
> >> >> >>> // set up whatever tables you need to
> >> >> >>> // etc.
> >> >> >>> })
> >> >> >>> }
> >> >> >>> }
> >> >> >>> ```
> >> >> >>>
> >> >> >>> Or maybe, a large lookup table that takes a while to build, and
> >> >> >>> might
> >> >> >>> not even be used, so you don't want to do it on load?
> >> >> >>>
> >> >> >>> ```js
> >> >> >>> var table
> >> >> >>>
> >> >> >>> function initTable() {
> >> >> >>> if (table) return
> >> >> >>> table = new Array(10000)
> >> >> >>> // do some expensive calculations
> >> >> >>> }
> >> >> >>> ```
> >> >> >>>
> >> >> >>> Things you don't want to initialize right away because
> >> >> >>> initialization
> >> >> >>> is expensive and/or the value might not even be used. That's the
> >> >> >>> problem I'm aiming to solve, and it's something I feel would be
> >> >> >>> useful
> >> >> >>> in its own right in the language, about equal in importance to
> weak
> >> >> >>> references. (Slightly specialized, but the need is not non-zero.)
> >> >> >>>
> >> >> >>> [1]: https://en.wikipedia.org/wiki/Lazy_initialization
> >> >> >>> [2]:
> >> >> >>>
> >> >> >>>
> >> >> >>> https://stackoverflow.com/questions/978759/what-is-lazy-
> initialization-and-why-is-it-useful
> >> >> >>> -----
> >> >> >>>
> >> >> >>> Isiah Meadows
> >> >> >>> m...@isiahmeadows.com
> >> >> >>>
> >> >> >>> 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 12:23 PM, Andrea Giammarchi
> >> >> >>> <andrea.giammar...@gmail.com> wrote:
> >> >> >>> > 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
> >> >> >>> > <isiahmead...@gmail.com>
> >> >> >>> > 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
> >> >> >>> >> m...@isiahmeadows.com
> >> >> >>> >>
> >> >> >>> >> 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
> >> >> >>> >> <andrea.giammar...@gmail.com> 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
> >> >> >>> >> > <isiahmead...@gmail.com>
> >> >> >>> >> > 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
> >> >> >>> >> >> m...@isiahmeadows.com
> >> >> >>> >> >>
> >> >> >>> >> >> 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
> >> >> >>> >> >> <andrea.giammar...@gmail.com> 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
> >> >> >>> >> >> > <isiahmead...@gmail.com>
> >> >> >>> >> >> > 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
> >> >> >>> >> >> >> m...@isiahmeadows.com
> >> >> >>> >> >> >>
> >> >> >>> >> >> >> Looking for web consulting? Or a new website?
> >> >> >>> >> >> >> Send me an email and we can get started.
> >> >> >>> >> >> >> www.isiahmeadows.com
> >> >> >>> >> >> >> _______________________________________________
> >> >> >>> >> >> >> es-discuss mailing list
> >> >> >>> >> >> >> es-discuss@mozilla.org
> >> >> >>> >> >> >> https://mail.mozilla.org/listinfo/es-discuss
> >> >> >>> >> >> >
> >> >> >>> >> >> >
> >> >> >>> >> >
> >> >> >>> >> >
> >> >> >>> >
> >> >> >>> >
> >> >> >>
> >> >> >>
> >> >> >
> >> >
> >> >
> >>
> >> -----
> >>
> >> Isiah Meadows
> >> m...@isiahmeadows.com
> >>
> >> Looking for web consulting? Or a new website?
> >> Send me an email and we can get started.
> >> www.isiahmeadows.com
> >
> >
>
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