Use cases for WeakMap

Erik Corry erik.corry at
Mon May 16 00:18:34 PDT 2011

2011/5/16 Brendan Eich <brendan at>:
> On May 16, 2011, at 12:01 AM, Brendan Eich wrote:
>> On May 15, 2011, at 11:55 PM, Erik Corry wrote:
>>> 2011/5/16 Brendan Eich <brendan at>:
>>>> Not if the object is frozen.
>>> That shouldn't prevent you adding private names.  See earlier message
>>> in this thread.
>> Frozen means [[Extensible]] is false, so you can't add any properties, ...
> I'll go further: frozen means the implementation should be free to move the object and anything associated with its shallow-frozen key/value state into read-only memory, so the full force of 50-year-plus OS and hardware MMU protection can ensure [[Extensible]] really is false.

I think this would also preclude the most efficient implementation of
Weak Maps.  In fact I have a hard time seeing how you would GC weak
maps at all under these conditions.

Erik Corry

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