On Apr 24, 2014, at 12:38 PM, Mark S. Miller wrote:
> I agree that this issue should treat for/of and [...x], etc, similarly.
> Either do both or neither.
>
> Does it alleviate the performance concerns if the .return is only invoked on
> early exit, i.e., before the iterator reports that it is done? For builtins
> like [...x], and for javascript code that has no statically apparent early
> exit, we'd know that the only remaining early exit possibility is a throw,
> which we already allow to be much slower.
Mark, I'm quite convinced that it is only early exists (including exceptions
originating within the loop) that need the @@return call. For any normal loop
exist, the iterator will have reported {done: true} and it is the iterators
responsibility to do the cleanup in that case. If the iterator is a generator
with a finally block to do the cleanup, the finally will have already been
triggered by the return that produced the {done:true} result
Allen
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