On Jun 28, 2011, at 5:45 PM, Axel Rauschmayer wrote: >> But before you've created an instance, it is pretty handy to have the >> constructor bound to a name so you can get to it. I don't think making the >> named object be the constructor means that they're *more* important, just >> that you generally have to go through them *first* to get to an instance. >> They get the name because they're the entrypoint. > > It depends on how you view instance creation: > > Prototypes-as-classes: new C() means:
If there are arguments in between the ( and ), they are passed to o.constructor. > (1) Create an instance o whose prototype is C. > (2) Initialize the new instance via o.constructor(). What if o.constructor returns another object than o? See below > Constructor functions: new C() means: > (1) Create an instance o whose prototype is C.prototype. > (2) Initialize it via the body of the constructor function (with |this| set > up properly). Step (2) could be exactly the same as the previous step (2), modulo the forgotten feature which is needed in both cases: For a function C in JS today, the return value if an object trumps the new instance (and engines actually avoid creating a new instance if it isn't needed for this reason). So there's more to it than this two-step procedure. > > Thus: > - Prototypes-as-classes: step (1) determines the name of the class (which – > to me – makes more sense for instanceof and subclassing) > - Constructor functions: step (2) determines the name of the class. I don't see how the step # determines the name of the class. That's backward. Rather, the two different choices of value bound to the name of the abstraction (prototype vs. constructor) determine the steps. The prototypes-as-classes approach makes new C(a,b) invoke C.constructor(a, b) with extra rules for object return value, which is a complexity. Especially for abstractions that want to be callable without 'new' to construct a new instance (Array, e.g.). Intuitions vary. There's nothing magically simpler about either approach. The |this| binding for the constructor invocation can be done in exactly the same way in both cases, but you left out the return value substitution feature. /be _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
