StopIteration, ForwardToTarget, ... & symbols

Brendan Eich brendan at
Mon Nov 26 17:27:27 PST 2012

David Bruant wrote:
> Le 26/11/2012 22:11, Brendan Eich a écrit :
>> Herby Vojčík wrote:
>>> Hi,
>>> shouldn't StopIteration, ForwardToTarget from "Notification proxies" 
>>> thread and similar ones be rather well-known unique symbols (like 
>>> @iterator), now that we have them, instead of well-known globals? \
>> Why?
>> Let's separate the naming and unique identity concerns. Objects have 
>> unique identity, so do symbols. But if a unique identity is required 
>> without being a property key, then an object is the right answer, not 
>> a symbol.
> I'm not sure not being a property key is that big of a constraint, so 
> I would say that objects and symbols are both valid equally valid.

Perhaps not, but it's odd to make a symbol just for (e.g.) immutability 
with no properties or [[Prototype]]. For realm-independence is more 
interesting. More below, on your good point I had forgotten momentarily 
in replying to Allen a minute ago.

>> I think this applies to StopIteration.
> It is suggested on the strawman that StopIteration be a constructor 
> [1] and I support this idea for StopIteration because an iterator may 
> have different reasons to stop and building instances with a message 
> (or any property) attached.

Yes, indeed, and StopIteration as constructor is used implicitly when a 
generator function returns a value. This makes the case for object not 
symbol. isStopIteration copes with realm-dependence.

> I'm not sure It'd be as relevant for ForwardToTarget.

I leave that to you and Tom :-P.



> David
> [1]
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