Thank you all so much for the feedback! The push-back has given me something to more to consider.
I’d like to add a couple points which are hopefully clarifying, but I do acknowledge the idea doesn’t seem to be attracting positive interest in its current form. I meant to note in the original gist that this isn’t a unique idea. Scala (and possibly others) do something very similar. The `apply` symbol was chosen for this example based on the name of the apply method from Scala. However, not being a Scala developer myself, I am cautious about accidentally attaching any baggage that may exist (unknown to me) in Scala’s solution to this proposal. To Jordan’s points - I would hope that the proposal could be scoped such that the impacts mentioned were not so significant. It certainly wasn’t the intent to make functions un-callable, for example. I would need to understand ES details a bit better to fully work through the objections raised (though this has motivated me to do so!). The proposal provides a very tactical example and one that I run into all the time (but perhaps I’m in a minority there). I should add a more strategic motivation to the proposal. The broader intent was to allow even better interaction between the functional and OO coding styles are common in ES. A function and an object are clearly not interchangeable in every situation. However there are many situations where they could be - conceptually. The proposal would help facilitate that. Lastly, regarding other ways to accomplish this, I usually end up expecting a function in the consumer. Dependencies then either need to be written as functions (usually higher-order functions to account for dependency injection), or wrapped by a function when provided to a consumer. So, something like this: ```js // class-based const userCreator = new UserCreator(userRepository); class UserSignupHandler { constructor(createUserFn) { this.createUser = createUserFn; } handle(userName) { return this.createUser(userName); } } const handler = new UserSignupHandler( u => userCreator.create(u) ); ``` This is not too bad, syntactically, and gets ever better if the bind-operator proposal goes through. But the frequency with which I find myself doing led to this proposal. I’m happy to hear any additional feedback others may have. > On Jan 27, 2019, at 11:36 PM, Ron Buckton <ron.buck...@microsoft.com> wrote: > > There’s nothing in that proposal says that an object with a `Symbol.apply` > has to have a different `typeof`. It *would* mean that any Call might require > additional dispatch which could have performance implications. It could also > be an approach to support “callable” classes: > > ```js > class Foo { > constructor() { /* constructor behavior */ } > static [Symbol.apply]() { /* call behavior */ } > } > ``` > > From: es-discuss <es-discuss-boun...@mozilla.org> On Behalf Of Jordan Harband > Sent: Sunday, January 27, 2019 9:35 PM > To: Brasten Sager <bras...@brasten.me> > Cc: es-discuss <es-discuss@mozilla.org> > Subject: Re: Proposal: Default object method > > Something that can be invoked has a `[[Call]]` slot, and is `typeof` > "function". > > Adding a Symbol that makes something callable would have a number of effects > - it would make `typeof` (one of the most robust operations in the language) > unsafe, because it would have to access the Symbol method, which could be a > throwing getter (or even one that just logs how many typeofs are called on > it). Additionally, it would mean any object could become callable, and any > function could be made *un* callable. > > This seems like a pretty large change, solely to avoid "classes with a single > method", which arguably should just be a function in the first place. > > On Sun, Jan 27, 2019 at 4:05 PM Brasten Sager <bras...@brasten.me > <mailto:bras...@brasten.me>> wrote: > Apologies if this has been raised before. I was unable to locate anything > similar. > > Any thoughts or ideas on this proposal would be appreciated! > > Original: https://gist.github.com/brasten/f87b9bb470973dd5ee9de0760f1c81c7 > <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgist.github.com%2Fbrasten%2Ff87b9bb470973dd5ee9de0760f1c81c7&data=02%7C01%7Cron.buckton%40microsoft.com%7C8c644033cebc48cdb58708d684e27a3d%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636842505603533257&sdata=qHxOcUdMF1i1QPc%2BZKC96Qq4%2BjQY1cgo7GBwDQ5f64Y%3D&reserved=0> > > -Brasten > > — > > # Proposal: Default object method # > > Objects w/ default method can be invoked like a function. > > ## Problem ## > > Objects that are well constrained (single responsibility) > can tend to end up with a single method, or at least a single method > that is important to most consumers. These methods tend to be named > by either verbing the class name (eg. `UserCreator.create()`) or with > some generic `handle` / `perform` / `doTheObviousThing`. > > Whatever the name, downstream consumers of the object end up coupled to > two implementation details: > > 1) this thing-doer is an object and not a function > 2) this thing-doer's doing method is called `X` > > ### Example ### > > Here we are going to create an object that can be used to > create a user later. Note that downstream consumers will only > care that this object does one thing: create a user. While it > make have other methods eventually for use in some limited > contexts, creating a user is its primary (and often sole-) > responsibility. > > ```js > class UserCreator { > constructor(repository) { > this.repository = repository; > } > > create(name) { > return this.repository.createUser(name); > } > } > > const userCreator = new UserCreator(userRepository); > ``` > > At this point, the `userCreator` is just a single-method object. > It is useful for injecting into other objects that may need to > create a user. But the fact that the `userCreator` is an object > with a single useful method is an implementation detail to which > consumers become coupled. > > ```js > > // Consumer of `userCreator`. Although this could itself be a > // good example of a "UserCreator"-like object (due to `.handle()`). > // > class UserSignupHandler { > constructor(userCreator) { > this.userCreator = userCreator; > } > > handle(userName) { > // UserSignupHandler is aware of ".create" when it really doesn't have to > be. > // > return this.userCreator.create(userName); > } > } > > const handler = new UserSignupHandler(userCreator); > ``` > > Notably, if we were to change the implementation of UserCreator later to be > a pure function, we would have to change all consumers of UserCreator when > conceptually it shouldn't be needed. There is still a thing-doer that has > the same input/output. > > > ## Proposed Solution ## > > An object instance can have a default method. This would allow an > object to be "invoked" exactly like a function, hiding the implementation > detail from consumers. > > Note that there are several ways to define how the default method is > determined, and this proposal is less concerned with this aspect than with > what it looks like to invoke the object. We will demonstrate an option here, > but alternatives are welcome. > > ```js > // This particular implementataion would use a Symbol. > // > > class UserCreator { > constructor(repository) { > this.repository = repository; > } > > [Symbol.apply](name) { > return this.repository.createUser(name); > } > } > > const userCreator = new UserCreator(userRepository); > > class UserSignupHandler { > constructor(userCreator) { > // NOTE: at the consumer, it almost makes more sense to > // name these with action verbs, as is done here. > // > this.createUser = userCreator; > } > > handle(userName) { > // UserSignupHandler is no longer coupled to the implementation details > it doesn't need. > // > return this.createUser(userName); > } > } > > const handler = new UserSignupHandler(userCreator); > ``` > > _______________________________________________ > es-discuss mailing list > es-discuss@mozilla.org <mailto:es-discuss@mozilla.org> > https://mail.mozilla.org/listinfo/es-discuss > <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmail.mozilla.org%2Flistinfo%2Fes-discuss&data=02%7C01%7Cron.buckton%40microsoft.com%7C8c644033cebc48cdb58708d684e27a3d%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636842505603533257&sdata=aka94qZafmZwTNsAjMMC%2FTvTww5P5sn4cSRmVdSe2yk%3D&reserved=0>
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