Le 12 juin 2013 à 12:55, Andreas Rossberg <[email protected]> a écrit :
> On 11 June 2013 21:19, Brendan Eich <[email protected]> wrote: >> Andreas Rossberg wrote: >>> >>> That makes a terrible API, though. I think Axel has a valid point that >>> the distinction between iterators and iterables is fuzzy enough to be >>> more confusing and error-prone than useful. >> >> Have you actually used Python or JS1.7 much, though? >> >> Have to ask, since throwing "confusing" and "error-prone" charges demands >> evidence or at least anecdotes. > > It is confusing me, for one -- I don't really understand the > difference anymore, nor the intended use cases. Granted, I might be > the only one confused. I'm not ready to believe that, though. ;) > > You see, initially the iterator proposals tried to suggest a simple > and understandable model: iterators were objects with a 'next' method, > iterables were objects with an @@iterator method that produces an > iterator. But neither is true anymore: > > - Iterators are iterables, they are supposed to have a 'next', > optionally a 'throw', and an @@iterator method that returns itself. > That is, the iterator interface has become considerably more > complicated and is mutually intertwined with iterables. > > - Iterables are iterators most of the time, except when they aren't. > Their @@iterator method may produce a new iterator or, in most cases, > not. That is, there is no useful contract of what an iterable is, and > it is useless as a concept to implement abstractions against. > Nevertheless, people will probably try, and then build something that > does not reliably work for all iterables. Thus error-prone. > > Where things stand now, the only reason we have @@iterator at all is > as a hook to provide implicit user-defined conversions from objects to > iterators, invoked by the for-of loop (and by extension, yield*). > > We could simplify spec _and_ programmers' life by explicitly > recognizing it as such. That is, for-of invokes a ToIterator > conversion meta function, which is the identity for any 'nextable', > and tries to invoke @@iterator for others. Thereby drop the misleading > notion of iterable, and drop the weird requirement for iterators to be > iterables themselves. > > WDYT? > > /Andreas Well, as currently specced, the operation that serves as `ToIterator` conversion meta function is: itr => itr[@@iterator]() If I understand you correctly, you propose that it should be changed to: itr => @@iterator in itr ? itr[@@iterator]() : itr The only place where it would simplify programmers' life, is where they try to define manually an iterator, which I expect to be quite rare. On the other hand, I see a small advantage of the "weird" requirement for iterators to be iterables themselves: It allows to discriminate between true iterators and merely "nextable" objects. ―Claude > _______________________________________________ > 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
