What are Symbols? Objects? New primitive type?

David Bruant bruant.d at gmail.com
Sun Apr 14 05:50:20 PDT 2013


Le 13/04/2013 09:31, Andreas Rossberg a écrit :
> On 13 April 2013 00:12, Brandon Benvie <bbenvie at mozilla.com> wrote:
>> 3.) A new type of primitive along with a new type of wrapper. In this case
>> we use the String/Number/Boolean precedent where `Symbol()` and `new
>> Symbol()` produce different kinds of results. The problem here is the
>> confusion that comes with ToString/ToPropertyKey when called on a Symbol
>> wrapper. What does `obj[new Symbol] = 5` do, for example? It allows footguns
>> like `obj[key + '_ext']` to silently do the wrong thing.
> That was the consensus at the last meeting, and it's already
> implemented in V8. The decision included that
> Symbol.prototype.toString is poisoned, i.e., any attempt to implicitly
> convert a symbol or a wrapped symbol to a string will throw, including
> both of your examples.
Just to clarify, implicit conversion is the behavior of ToString (ES5.1 
- 9.8 with Table 13), not Symbol.prototype.toString. And that's what I 
read from the notes too. Do you confirm?
Apparently, symbols have a [[name]] [1]. It would be good if they even 
had a public "name" property (or rather Symbol.prototype.name getter) at 
least for debugging purposes. It would make sense if 
Symbol.prototype.toString (when called explicitly) returned symbol.name.

David

[1] 
http://wiki.ecmascript.org/doku.php?id=harmony:function_name_property#symbols


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