On Feb 2, 2015, at 9:11 AM, Domenic Denicola wrote: > I don’t think we should be assuming that an abnormal completion should run > anything like the same logic as a normal completion. If I understand > correctly, that’s what any proposal to fall back to “close” does.
"close" exists to deal with abnormal loop completion (or consumption completion, in general). A for-of loop only class "close" on its iterator, if something happens (exception, return, break) to terminate the loop before its iterator is exhausted. That is exactly what is happening if yield* throws because of a "protocol violation" for the situation we are talking about. yield*, just like for-of, doesn't call "close" on a normal (the inner iterator was exhausted) completion. Allen > > From: es-discuss [mailto:[email protected]] On Behalf Of Allen > Wirfs-Brock > Sent: Monday, February 2, 2015 12:09 > To: Jason Orendorff > Cc: es-discuss list; [email protected]; Erik Arvidsson > Subject: Re: a weird yield* edge case > > > On Feb 2, 2015, at 7:26 AM, Jason Orendorff wrote: > > > On Sat, Jan 31, 2015 at 10:56 AM, Erik Arvidsson <[email protected]> > wrote: > Another option would be to throw. Then the caller can tell that they did > something that was not expected by the inner iterator. > > > I agree. In fact, isn't this required by transparency? > > Inner().throw() in this situation would throw a TypeError (since there's no > such method). So wrapper().throw() should throw a TypeError. > > Except that a consumer (such as for-of) is expected to check for the > existence of 'throw' before trying to invoke it. That's really where the > transparency is lost in this case. > > But I agree that throwing to indicate a "protocol violation" seems like a > good approach. but it could mean that Inner doesn't get properly "closed". > How how about this variation: > > 2a) An TypeError exception is thrown, but first 'close' (if it is present) is > invoked on the yield* target iterator. > > That would seem to both satisfy the 'close' contract (a consumer (in this > case yield*) calls it if is terminating its use of an iterator before the > "done" state is reached) and produces an exception to the wrapper consumer > for the "throw" protocol violation. > > Allen > > > > > > > > > > > -j > >
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