On Nov 14, 2011, at 3:09 PM, Axel Rauschmayer wrote:
>
>> The concept of a constructor function being the "class" of an object is one
>> of those things that has been around JS apparently from the beginning. It
>> just didn't have a suggestively named operator. However an object is
>> instantiated, this operator is simply reporting that the "class"of the
>> object whatever is accessible as the object's "constructor".
>
>
> So you don’t think the two roles clash semantically? (1) “Turn an object
> exemplar into a class” versus (1) “get the class of an object”. Both are
> definitely useful! But that they can be performed by the same operator seems
> like a happy coincidence. If (1) was to be further refined, e.g., as Brendan
> suggested, by throwing an exception if an object exemplar does not have a
> "constructor" method then it seems both roles would drift further apart. I’m
> mainly arguing for a clear separation of concerns.
The two roles are the same! The value of the constructor property of an object
exemplar is a function exemplar (AKA class exemplar) whose prototype
property's value is the object exemplar. When you say:
let P = class {constructor() {} };
You aren't turning an object exemplar into a class exemplar your are simply
accessing the class exemplar that is explicitly defined as part of the object
exemplar.
The above let is also equivalent to:
let PrototypalP = {constructor(){} };
let P = class PrototypalP;
which is equivalent to:
let P = class {constructor(){} };
let PrototypalP = P.prototype;
Finally, when I talk about an object's constructor I include the possibility
that 'constructor' is inherited, so the above identifies only hold when an own
constructor property is explicitly provided. In fact, that is really what I
mean by an object exemplar
var foo = { };
class foo is Object; //true
Object.prototype is foo; //also true
bar = new foo; //same as new foo.constructor which is the same as new Object
class bar is class foo; //and both === Object.
It all falls out of the plumbing.
Allen
>
> --
> Dr. Axel Rauschmayer
> [email protected]
>
> home: rauschma.de
> twitter: twitter.com/rauschma
> blog: 2ality.com
>
>
>
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