Object ID's

[P T Withington]

On 2007-03-20, at 21:09 EDT, Lars T Hansen wrote:

>>
>> It *feels* more critical than the lambda syntax that is getting so
>> much attention in the other current thread.
>
> Amen to that, though there are several kinds of dictionary types one
> could discuss, from the simple property-less object type (more
> primitive than Object) to elaborate dictionary classes.

The last time this came up, I said:

> On 2007-01-05, at 20:14 EST, Brendan Eich wrote:
>> Another item falling out of the ES4 spec: hashes mapping string to  
>> value where the mapping is not polluted by Object.prototype.  A  
>> late "save" may be possible, if anyone can suggest syntax.  E.g.,  
>> var hash = #{'foo':1, 'bar':2, 'baz':3}; alert('toString' in hash)  
>> => false.  Eek, yet another attempt to use #.
>
> Since you can't build a pure hash in Javascript, this would be a  
> _highly_ desirable addition.  Naive use of Object for hash has been  
> the source of a number of subtle bugs in our code.  One might even  
> be so bold as to make Hash the primitive and Object inherit from it?
>
> We would have many uses for Hash in our code base.  I have defined  
> a dictionary class that I use for some cases, but often have had to  
> trade correctness for performance.
>
> A literal syntax would not be that important if you could have a  
> constructor with named arguments.  (Because the constructor's  
> `arguments` property would be a Hash?)  It would also be useful to  
> have a constructor that constructed a new hash from an existing one.
>
>> (Should these map value to value, rather than string to value?   
>> E4X (ECMA 357) already introduced QName objects as identifiers, so  
>> one can't pretend all properties are named by strings, if one  
>> believes in E4X.)
>
> value -> value would be a bonus that I would greatly appreciate,  
> but then won't you need to define a protocol for extending hash- 
> code computation and `===`?

I think having a pollution-free dictionary type would be much more  
important that the `=>` syntax shortcut.  Having a dictionary that  
can map values to values would be a bonus, but also important.  You  
can't do either of these things efficiently in the language, which is  
a good reason to make them built in.