What are Symbols? Objects? New primitive type?

Brandon Benvie bbenvie at mozilla.com
Sat Apr 13 06:26:16 PDT 2013


On 4/13/2013 12:31 AM, Andreas Rossberg wrote:
> 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. So no footgun, which I agree is important.
> (Object.prototype.toString is not on that path, however, so can treat
> symbols separately.)
>
> I'm a bit confused about some bits of Allen's comment on your Gist,
> though, which don't line up with what I thought we decided on. In
> particular, ToObject(symbol) should be perfectly fine and creates a
> wrapper object. Similarly, Symbol()["foo"] auto-converts to a wrapper
> object and returns undefined as usual, and new Symbol() directly
> creates a wrapper object.
>
> /Andreas
This would be the reason I created this thread: there was at least two 
different interpretations of the outcome of the meeting by people who 
were at the meeting, and a third one (mine) that came from reading the 
meeting notes. From that I surmised it would be good to, at the very 
least, figure out which one of the three is an accurate reflection of 
what was actually to be the final version.


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