Hi, A re-ping on this issue. Probably the relevant people were distracted by TC39 last week.
On Tue 08 Apr 2014 14:47, Andy Wingo <[email protected]> writes: > Hello, > > The current ES6 draft seems to specify that if a running generator > throws an exception, that its state moves to "completed". It seems to > specify this in ยง25.3.3.1, `GeneratorStart'. (Oddly, the procedure > described in `GeneratorResume' can return to `GeneratorStart'; spec > strangeness). Anyway, that means that: > > function *foo() { yield 1; yield 2 } > var iter = foo() > iter.next() // => { value: 1, done: false } > iter.throw(42) // uncaught exception: 42 > > Up to here all good. And then we have, according to the spec: > > iter.next() // => { value: undefined, done: true } > > I find this very strange. I would have expected an exception of the > kind "generator is already running", as indeed we entered the running > state but never moved out of that state. > > I think that nonlocal exits from within generators should not move the > state to "completed", and should leave them as "suspendedStart". Beyond > a subjective impression of strangeness, which not all may share, this > part of the specification requires that the continuation of all > GeneratorResume() invocations include a try/catch to set the generator > state to "completed" if the activation resumes and then exits > nonlocally. > > Of course using "iter.throw" is the easy way to cause an exception, but > it could happen within some function called by the generator. But if we > decide to remove the try/catch from around the GeneratorResume, it might > make sense to also remove the suspendedStart -> completed transition > that is special-cased in Generator.prototype.throw. > > In summary: the completed-on-exception state change is of little utility > but causes overhead in generator implementations in the form of the > mandatory try/catch around GeneratorResume and so it should be removed > IMO. > > If it is removed we could also consider removing the > suspendedStart->completed state change on Generator.prototype.throw. If > that were done we could remove the suspendedStart state entirely; dead > spec elimination ;) > > WDYT? > > Regards, > > Andy > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
