Normative: iterator helpers close receiver on argument validation failure #3467
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bakkot
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ljharb
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Nov 12, 2024
ljharb
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normative change
| 1. Let _numLimit_ be Completion(ToNumber(_limit_)). | ||
| 1. IfAbruptCloseIterator(_numLimit_, _iterated_). | ||
| 1. If _numLimit_ is *NaN*, then | ||
| 1. Let _error_ be ThrowCompletion(a newly created *RangeError* object). |
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I would inline these ThrowCompletions into the IteratorClose calls.
michaelficarra
approved these changes
Nov 21, 2024
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The general rule when working with iterators / iterables is that once you get an iterator it is your responsibility to close it when you're done with it, unless it errors out or completes. We're consistent about this when we get the iterator from an iterable, and in some of the places where we get the iterator directly (e.g. in
Set.prototype.isDisjointFromstep 5.c.ii.1.a), but as pointed out by @zloirock, iterator helpers don't close their receiver when one of their argument is invalid. Since iterator helpers are conceptually "take ownership" of their receiver (either by consuming it fully, or by closing the receiver when the iterator helper itself is closed), and since an argument failing validation is not an error of the underlying iterator, helpers should close their receiver in this case to be consistent with the general rule above.Unfortunately
IfAbruptCloseIteratorandIteratorCloseboth take an Iterator Record, not the iterator object itself, and we don't construct the Iterator Record until after argument validation. So we have to make a "partial" Iterator Record for use by these methods. (It's still a well-typed Iterator Record.) This is a spec fiction to simplify the spec text and doesn't need to correspond to anything in an actual implementation.