April 10 2014 Meeting Notes

[Allen Wirfs-Brock]

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