On Tue, Apr 15, 2014 at 10:24 AM, Andreas Rossberg <[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.
I think the concern was more about the implicit throw than the implicit try-catch. That is, the StopIteration protocol required not only being prepared to catch an exception, but *actually throwing and catching an exception* at the end of every for-of loop. In SpiderMonkey, at least, throwing an exception is a performance cliff. It can involve re-compiling code in a less optimized mode---that kind of thing. A try-catch is not so bad. Some optimizations like phi elimination are less aggressive, which we think probably doesn't matter much. Also, a function that contains a try-catch can't be inlined at the moment--but that could be fixed, and it's even less likely to matter here. -j _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
