> I would like to point out that this particular example could be done in terms of existing proxies ...
Yes, for this simplistic case that you properly mentioned, operation `[]` is enough, but when i writing that example I rather keep in mind js [Map]( https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Map) and object keys. So the goal is also simplified syntax of accessing and mutating maps, like: ```js var map = new Map(); var key = {foo: "bar"}; var val = {some: "value"}; map(key) = val; // same as map.set(key, val) if "`_()=_`" operation would be properly implemented on Map console.assert(map(key) === val); // same as (map.get(key) === val) map.delete(key); console.assert(map(key) == null); ``` If `"_()=_"` operation will be available in language, then anyone will be able to implement his own `MultiDimMap` multidimensional map (on top of existing single-dimensional map), with usage similar to following ```js var map = new MultiDimMap(); var key0 = {foo: "bar"}; var key1 = {foo1: "bar1"}; var val = {some: "value"}; map(key0, key1) = val; console.assert(map(key0, key1) === val); map.delete(key0, key1); console.assert(map(key0, key1) == null); ``` Also to provide more complete information about current state of similar feature in other languages, it would be good to take a look on [C# indexers](https://msdn.microsoft.com/en-us/library/6x16t2tx.aspx). It also provides extensive possibility to implement `"_[]=_"` operation with arbitrary number of arguments, so in case of C# expressions like `obj.idxr[arg1, arg2, ... , argN] = val` is pretty valid (if `obj.idxr` indexer properly implemented in `obj`). But this feature looks for me more ambiguous with current implementation of Proxy object (more specifically with current definition of `set` and `get` methods of [proxy handler]( https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/handler)). In particular `set` states signature: ``` set: function(target, property, value, receiver) ``` but if we will have a list of arguments (like `obj[arg1, ... , argN]`) then what should be passed to `property` argument, if it will be `property == [arg1, ... , argN]` then it looks like OK, but if we pass only one argument, like `obj[Array.from(arg1, ... , argN)]` what should be in `property` , of course it should be rather `property == [ [arg1, ... , argN] ]` but still it looks little bit ambiguous. So for me [Scala](http://docs.scala-lang.org/cheatsheets/) approach for "indexing" with `"()"` / `"()="` operations looks more nice. (More information about Scala approach to `apply`/`update` - `"()"` / `"()="` can be found at https://www.scala-academy.com/tutorials/scala-apply-update-methods-tutorial, also about maps: https://www.safaribooksonline.com/library/view/scala-cookbook/9781449340292/ch11s15.html, http://docs.scala-lang.org/overviews/collections/maps#operations-in-class-mutablemap ) On 13 May 2016 at 20:29, Isiah Meadows <[email protected]> wrote: > I would like to point out that this particular example could be done in > terms of existing proxies now: > > ```js > var sttFunc = new Proxy({}, { > get(target, key) { > console.log("get: [", key, "]"); > return key; > }, > set(target, key, value) { > console.log("set: [", key, "] = ", val); > return true; // success > } > }); > > // Usage: > sttFunc["key"] = "value"; // set: [key] = value > sttFunc["key"]; // get: [key] > ``` > > On Thu, May 12, 2016, 15:02 Jason Orendorff <[email protected]> > wrote: > >> The nice thing about @@symbol-named methods is that we *don't* have to >> extend the Proxy API for them. They're just method calls. >> >> This is why there's no hasInstance Proxy trap. `instanceof` basically >> boils down to a method call, and we already have Proxy traps for >> method calls: `get` and `apply`. >> >> It's a good thing, too, because adding a new Proxy trap is a last >> resort. Just from a conceptual standpoint, the less complicated >> objects are, the better; just because there are 14 *fundamental* >> operations on objects doesn't mean we're eager to add more. But >> there's also an inherent compatibility issue. Whenever you add a new >> trap, the deal is, all existing Proxy handlers were written without >> consideration for the new operation. So old code, used in combination >> with the new language feature, would tend to break. >> >> Cheers, >> -j >> >> >> On Thu, May 12, 2016 at 9:42 AM, Igor Baklan <[email protected]> wrote: >> > It would be nice to "bring sense" to expressions like "obj(a1, ... , >> aN) = >> > val". (like "obj(x) = y") >> > In Scala langue it defined in pretty clear and simple way: >> > >> > "obj(a1, ... , aN)" <==> "obj.apply(a1, ... , aN)" >> > "obj(a1, ... , an) = val" <==> "obj.update(a1, ... , aN, val)" >> > >> > Of course this applied only to that cases when obj was not defined like >> > method (in case of regular methods "mth(args) = val" will cause compile >> time >> > error). >> > So in Scala even arrays and maps are accessed and updated using "()" >> > operator >> > >> > js( arr[index] = val ) <==> scala( arr(index) = val ) >> > >> > (see http://www.scala-lang.org/api/2.10.0/index.html#scala.Array , >> > >> http://docs.scala-lang.org/overviews/collections/maps#operations-in-class-mutablemap >> > , etc) >> > >> > So the proposals are: >> > >> > (1) to introduce symbols like @@apply and @@update with very similar to >> > Scala meaning (for cases when 'obj.sttFunc' is not a function) >> > >> > "obj.sttFunc(a1, ... , aN) = val" ==> "obj.sttFunc[Symbol.update] >> > (obj.sttFunc, obj, [a1, ... , aN], val)" >> > "obj.sttFunc(a1, ... , aN)" ==> "obj.sttFunc[Symbol.apply] >> (obj.sttFunc, >> > obj, [a1, ... , aN])" >> > >> > (2) to extend Prxoy object specification to support update action along >> with >> > apply action: >> > >> > I would like to write something similar to >> > >> > var target = { >> > jsApply: function(key){ >> > console.log("apply: ", key); >> > return key; >> > }, >> > jsUpdate: function(key, val){ >> > console.log("update: (", key, ") = ", val); >> > return val; >> > } >> > }; >> > var sttFunc = new Proxy(target, { >> > apply: function(target, thisArg, argumentsList) { >> > target.jsApply.apply(thisArg, argumentsList); >> > }, >> > update: function(target, thisArg, argumentsList, assignValue) { >> > target.jsApply.apply(thisArg, >> > Array.from(argumentsList).concat([assignValue])); >> > } >> > }); >> > >> > And then run it as following >> > >> >> sttFunc ("key") = "value"; >> > >> > update: ( key ) = value >> > >> >> sttFunc ("key"); >> > >> > apply: key >> > "key" >> > >> > >> > _______________________________________________ >> > 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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