Hi This proposal offers a way to get around some of the strange semantics of '=', specifically the way read-only properties and setters on objects in the prototype chain can restrict what you can do on the receiver of an assignment. However it has some strangeness itself:
* There is little point in having read-only properties if the common way to do assignment is :=. := will just walk all over a read-only property. * Copying private members from one object to another violates the encapsulation pretty badly. You would hope that using private names allowed you to easily reason about which objects have which properties, just by looking at the limited number of places a private name is used. But with this any code in the system that has two instances of a class can splat object a's private properties with those from object b. It's rather like a replay attack in crypto. * I don't understand the super stuff. Is there a typo here?: MyConstructor.prototype = Object.create(Baz); //inherit from Bar, not Foo On 7 August 2012 00:44, Allen Wirfs-Brock <[email protected]> wrote: > Based upon discussions last week in the "July 25, 2012 - TC39 Meeting Notes" > thread, I've created a new strawman proposal for a := operator. See > http://wiki.ecmascript.org/doku.php?id=strawman:define_properties_operator > > := is a convient way to copy properties from one object to another or to > extend an object with new properties. It combines supports for many of the > same use cases as the previously proposed "object extension literals" and > the JSFixed Object.extend proposal. > > The most important characteristic of := is that it uses > [[DefineOwnProperty]] semantics rather than [[Put]] semantics to define > properties on its target object so it doesn't run into issues with > assignment to accessor properties or over-riding inherited readonly > properties. It is also smart about dealing with methods that reference > super. > > Some basic examples: > > target := src; //define all own properties of src onto target > > //add a method and an accessor to an existing prototype > Point.prototype := { > plus(aPoint) {return new > this.comstructor(this.x+aPoint.x,this.y+aPoint.y}, > get rho() {return Math.sqrt(this.x*this.x+this.y*this.y} > }; > > > Have at it, > > Allen > > _______________________________________________ > 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
