Le 24/09/2011 22:00, François REMY a écrit : > What's the use case that justify it's good to change a prototype after > the object' initialization? Excellent question! We've been over this question in the "Standardizing __proto__" thread starting at [1] and the Firefox bug that triggered it [2]. Besides "subclassing" (which would be now solved with all the things I mentionned before), the only example I have heard of and consider being worth was [3] where there is GUI to create a JS environment. Here, I'm not 100% sure __proto__ is necessary, but it sure is handy to implement changing the prototype of an object dynamically.
David [1] https://mail.mozilla.org/pipermail/es-discuss/2011-March/013131.html [2] https://bugzilla.mozilla.org/show_bug.cgi?id=642500 [3] http://avocadojs.com/ > > > -----Message d'origine----- From: David Bruant > Sent: Saturday, September 24, 2011 9:54 PM > To: Xavier MONTILLET > Cc: [email protected] > Subject: Re: Function.create > > Le 24/09/2011 19:30, Xavier MONTILLET a écrit : >> I don't get the difference between the proto operator and some >> setPrototype method that could be added (or the actual __proto__ >> property)... > The proto operator works for initialization only on a newly created > object while __proto__ allows to change the prototype anytime. > ------ > var f = function(){}, a = []; > var o = {}; > > var f2 = o <| function(){}; // ok, new object created > var a2 = o <| []; // ok, new object created > > var f3 = o <| f; // throw an error, because f is already an object with > a prototype. Its prototype can't be changed dynamically > var a3 = o <| a; // throws for the same reason > > f.__proto__ = o; // prototype changed > a.__proto__ = o; // same > ------ > > David > >> >> On Sat, Sep 24, 2011 at 6:03 PM, David Bruant <[email protected]> >> wrote: >>> Le 24/09/2011 15:33, Jake Verbaten a écrit : >>>> There is no standardized way to create a new function with a prototype >>>> which is not Function.prototype. >>>> >>>> I propose Function.create >>>> >>>> /* >>>> Creates a new function whose prototype is proto. >>>> The function body is the same as the function fbody. >>>> The hash of propertydescriptors props is passed to >>>> defineproperties just like >>>> Object.create does. >>>> */ >>>> Function.create = (function() { >>>> var functionBody = function _getFunctionBody(f) { >>>> return f.toString().replace(/.+\{/, "").replace(/\}$/, ""); >>>> }; >>>> var letters = "abcdefghijklmnopqrstuvwxyz".split(""); >>>> >>>> return function _create(proto, fbody, props) { >>>> var parameters = letters.slice(0, fbody.length); >>>> parameters.push(functionBody(fbody)); >>>> var f = Function.apply(this, parameters); >>>> f.__proto__ = proto; >>>> Object.defineProperties(f, props); >>>> return f; >>>> }; >>>> })(); >>>> >>>> This is the same as Object.create except the second parameter is a >>>> function. >>>> >>>> It will create a new function whose function body is the same as the >>>> function passed in. >>>> >>>> I don't believe this is possible to do in ES5 without __proto__ >>> It is not indeed. >>> This topic has been discussed a couple of times here. There is one >>> proposal that is more generic than your solution which is the proto >>> operator [1]. >>> >>> Basically, to create a function with a chosen prototype, you can do: >>> ----- >>> var f = myProto <| function(a, b){return a+b;} >>> Object.getPrototypeOf(f); // myProto >>> f(1, 2); // 3 >>> ----- >>> >>> I'm a big fan of the proto operator proposal, however, as raised >>> previously this operator relies on the object being created to have an >>> intialisation syntax. This prevents, for instance, Date objects to have >>> a custom prototype with this method. I am not very familiar with it >>> yet, >>> but I think that if they ever came to life, ParallelArrays [2] would >>> suffer from the same problem. >>> By the way, could someone add this concern as a note ("open issue" or >>> "limitation" or something like this) in the proto operator page, >>> please? >>> >>> One even more generic way which would work even for objects that >>> have no >>> initialization syntax would to standardize one of [3] or [4]. Is >>> there a >>> wiki page mentionning these two functions somewhere? If not, may it be >>> added and linked in some way to the proto operator? >>> >>> David >>> >>> [1] http://wiki.ecmascript.org/doku.php?id=harmony:proto_operator >>> [2] >>> https://github.com/RiverTrail/RiverTrail/blob/15ae7f6f77d9d2842d9d75458017efd9fe0fbee7/jslib/ParallelArray.js#L29 >>> >>> [3] >>> https://mail.mozilla.org/pipermail/es-discuss/2011-March/013141.html >>> [4] >>> https://mail.mozilla.org/pipermail/es-discuss/2011-March/013154.html >>> _______________________________________________ >>> 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 _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
