Using weakmaps has disadvantages if instances are many, due pressure, and
it's also slower than just further property access, requiring a
`wm.get(...)` each time.
On top of that, you workaround the issue, but you don't solve it.
The platform way to solve your issue is the following:
```js
class Foo {
get bar() {
if (this.constructor.prototype === this) throw 'unauthorized';
var result = [];
Object.defineProperty(this, 'bar', {value: result});
return result;
}
}
```
I've used the long check instead of `this === Foo.prototype` because the
condition `this.constructor.prototype` works through inheritance chain too.
I also use a variable and return it instead because not everyone knows that
IE might go in recursion accessing a getter within the getter ;-)
Regards
On Mon, Sep 11, 2017 at 7:06 AM, Michał Wadas <[email protected]> wrote:
> BTW consider this:
>
> ```js
> class Foo {
> get bar() {
> Object.defineProperty(this, 'bar', {value: []});
> return this.bar;
> }
> }
> const a = new Foo;
> Foo.prototype.bar;
> const b = new Foo;
> const c = new Foo;
> // b.bar === c.bar
> ```
>
> So I recommend this instead:
>
> ```js
> const wm = new WeakMap;
> class Foo {
> get bar() {
> if (!wm.has(this)) {
> wm.set(this, []);
> }
> return wm.get(this);
> }
> }
> const a = new Foo;
> Foo.prototype.bar;
> const b = new Foo;
> const c = new Foo;
> // b.bar !== c.bar
> ```
>
>
> On Fri, Sep 1, 2017 at 12:11 PM, <[email protected]> wrote:
>
>>
>>
>> On August 31, 2017 6:15:20 PM GMT+02:00, Isiah Meadows <
>> [email protected]> wrote:
>> >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.
>>
>> But then, it seems to me Andrea's self-rewriting getter gets to the point.
>>
>> Maybe there can be 'caching' getter planned as in:
>>
>> Object.defineProperty(foo, "bar", {
>> get: () => "baz",
>> caching: true
>> });
>>
>> with a shortcut
>>
>> Object.defineLazyValue(
>> foo, "bar", () => "baz");
>>
>> which is implementable via a lib.
>>
>> Herby
>> >-----
>> >
>> >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
>> >_______________________________________________
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>>
>
>
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