Must built-in prototypes also be valid instances? (Was: Why DataView.prototype object's [[Class]] is "Object"?)

[Allen Wirfs-Brock]

On Sep 29, 2012, at 7:23 PM, Rick Waldron wrote:

> ...
> 
> Subjectively, the examples here are exactly how I would expect (hope?) this to behave, as the existing behaviour: 
> 
> > Array.prototype.push(1)
> 1
> > Array.prototype
> [ 1 ]
> 
> 
> ...Has always been seemed "strange" ;)
> 

I believe this is the root item we are discussing.   The legacy precedent says that Map.prototype.set("screwed", "you") should work and create an accessible map entry. 

I specified Map.prototype to throw.

> 
> 
> 
> 
> 
>  
> Your change requires implementations to provide a different built-in class (constructor/prototype) initialization path. That's not desirable _per se_. Neither IMHO is the user-facing semantic split among "old" and "new" constructors.
> 
> There are two separate issues here:
> 
> 1. Should Map.prototype be an instance (firstborn for its realm) of class Map?
> 
> 2. Should Map.prototype be a key/value store that can be used or abused as any other Map could be?
> 
> We should not mix these up. SpiderMonkey (and possibly V8, I haven't tested) says "yes" to 1 and "no" to 2.
> 
> 1: yes
> 2: no
> 

As I covered in my reply to Brendan, I don't think these are sufficiently defined to really answer.  But if you definition of "an instance" is that Object.prototype.toString.call(Map.prototype) returns "Map" then the latest spec. draft does 1: yes, 2: no

Allen
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