As a meta-point, I'd like for us to stop adding ".create()" functions, or at least stop adding them without syntax. The early precedent -- document.create() -- is an accident of C++ object ownership semantics from a DOM that often seems to be designed to be explicitly *un*-idiomatic. We have an allocator form (new) and we have factory functions (Array())…the third creation mechanism seems wholly incongruous.
Regards On Sep 24, 2011, at 10:40 AM, Oliver Hunt wrote: > I believe the goal is to eventually deprecate the magic of __proto__ as > mutating the prototype of an object makes it difficult to reason about a > program and supporting the mutation of an object's prototype also has a > reasonably significant performance cost -- the exact time and place (and > extent) of the cost is engine specific, but certainly it is not free. > > That said I'm not yet convinced we'll ever be able to kill it off :-/ > > --Oliver > > > On Sep 24, 2011, at 10:30 AM, Xavier MONTILLET wrote: > >> I don't get the difference between the proto operator and some >> setPrototype method that could be added (or the actual __proto__ >> property)... >> >> 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 -- Alex Russell [email protected] [email protected] [email protected] BE03 E88D EABB 2116 CC49 8259 CF78 E242 59C3 9723 _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
