That is why I'm proposing to use a getter, you don't have to reason about
the context in `lazy fullname() { return this.firstName + ' ' +
this.lastName; }` and it still works with de-contextualized invokes such
`lazy random: () => Math.random()` as long as you transpile that as getter
calling the right context (when/if needed).Both cases can de-sugar to same redefinition of a getter. Regards On Tue, Jun 12, 2018 at 10:56 AM, Aadit M Shah <[email protected]> wrote: > When the getter lives on a prototype it would install the memoized value > on this using [[Define]]. This is the same way it would work in regular > lazy getters: > > const defclass = prototype => { > const constructor = prototype.constructor; > constructor.prototype = prototype; > return constructor; > }; > > const Person = defclass({ > constructor: function Person(firstname, lastname) { > this.firstname = firstname; > this.lastname = lastname; > }, > lazy fullname: this.firstname + " " + this.lastname > }); > > const john = new Person("John", "Doe"); > const jane = new Person("Jane", "Doe"); > > console.log(john.fullname); // John Doe > console.log(jane.fullname); // Jane Doe > > Note that the this within the lazy property value expression (i.e. within > the expression this.firstname + " " + this.lastname) refers to the > instance (i.e. either john or jane). This can be confusing because > without the lazy keyword, this would refer to the lexical context. > Although I'm comfortable with it yet I'm open to other suggestions. > > > On Tue, Jun 12, 2018, at 3:31 AM, Jordan Harband wrote: > > How would this work when the getter lives on a prototype? (like most > builtin getters) Would it install the memoized value on `this`, or on the > object that contains the getter? Would it use [[Set]] or [[Define]]? > > On Tue, Jun 12, 2018 at 12:13 AM, Aadit M Shah <[email protected]> > wrote: > > > Hello TC39, > > I recently opened an issue <https://github.com/tc39/ecma262/issues/1223> in > the tc39/ecma262 <https://github.com/tc39/ecma262> repository, proposing > a new syntax for lazy getters, and I was directed to the CONTRIBUTING > <https://github.com/tc39/ecma262/blob/master/CONTRIBUTING.md> page which > stated that I should start a conversation on this mailing list. > > So, my feature proposal is to have syntactic sugar for creating lazy > getters > <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/get#Smart_self-overwriting_lazy_getters>. > To summarize my original proposal (which you can read by following the very > first link above), I find that creating lazy getters is very verbose. For > example, consider: > > const take = (n, xs) => n === 0 ? null : xs && { > head: xs.head, > get tail() { > delete this.tail; > return this.tail = take(n - 1, xs.tail); > } > }; > > My proposed solution is to add a new keyword lazy to the language. This > keyword can only be used as a prefix to longhand property names in object > initializers, and it defers the execution of the value expression until the > property is accessed. In short, it's just syntactic sugar for lazy getters: > > const take = (n, xs) => n === 0 ? null : xs && { > head: xs.head, > lazy tail: take(n - 1, xs.tail) > }; > > This is purely syntactic sugar. The semantics of this new syntax would > remain the same as that of the desugared syntax. In particular, calling > Object.getOwnPropertyDescriptor(list, "tail") would return an accessor > descriptor before accessing list.tail and a data descriptor afterwards. > > Furthermore, there are other advantages of having this syntactic sugar. > For example, creating cyclic data structures becomes much easier. Examples > are provided in my original proposal which is linked above. Hope to hear > your thoughts on this. > > Regards, > Aadit M Shah > > _______________________________________________ > 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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