On 15 April 2014 18:06, Allen Wirfs-Brock <[email protected]> wrote: >>> AWB: We _could_ add a `return()` method. >>> ... It's a bigger change, but we could make for-of invoke `return()` on exit >>> or completion >> >> This would be a _significant_ cost. One reason we got rid of the >> StopIteration protocol was the performance cost incurred by having to >> wrap all loops into implicit try-statements, which are costly. This >> proposal asks for re-introducing the same cost. > > Essentially it means that all generator based loops need to be wrapped in a > finally. Whether or not this has a significant cost or is a equivalent to an > exception handler depends upon implementation specific details of the > runtime design.
I'm very doubtful, given how VMs currently handle these features. I'm pretty sure the consequence will be that the golden new future with for-of and generators will be significantly slower than manual for-in or for-;; loops for a long time, if not forever. And consequently, adoption would suffer. And FWIW, it would have similar effects on yield* and generator expressions as well. (We already see a similar effect with higher-order array functions: we get regular complaints that they are slower than for-loops, but there is only so much we can do given their more expensive spec'ed semantics.) /Andreas _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
