The class operator: a bridge between object and function exemplers

Brendan Eich brendan at mozilla.com
Mon Nov 14 18:41:11 PST 2011


On Nov 14, 2011, at 6:36 PM, Axel Rauschmayer wrote:

>> Given this meaning of "class" when testing a value, I'm not sure if we can rescue the pun above by which we use the same operator to define a class. If forced to choose only one of these two roles for the "class" keyword, I'd prefer to use it only to define a class, not to test values. But having only just noticed this discrepancy, I am also not sure we cannot rescue the pun. Let's try.
> 
> Is a dual role even necessary? Why not stick to just class declaration? Looking through the eyes of an outsider, class { ... } looks like a class declaration. Given that we already have typeof and instanceof, wouldn’t an outsider expect a name such as classof? Furthermore, if object exemplars and function exemplars are to exist in parallel. Then:
> 
>      function Foo() {};
>      var f = new Foo();
>      classof f === Foo // true
> 
>      let Foo = {};
>      var f = new Foo();

This could succeed, due to 'constructor' inherited from Object.prototype. But, it could fail if we require an own constructor, or at least an inherited one whose value is a function object (or callable object if host) whose .prototpye is the exemplar.


>      classof f === Foo // true

If new Foo() throws, you won't reach here, and all is consistent.

/be

> 
> The above would not hold for `class`.
> 
> -- 
> Dr. Axel Rauschmayer
> axel at rauschma.de
> 
> home: rauschma.de
> twitter: twitter.com/rauschma
> blog: 2ality.com
> 
> 
> 

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