Normative: use Numbers instead of reals as counters in Iterator builtins#3776
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Normative: use Numbers instead of reals as counters in Iterator builtins#3776michaelficarra wants to merge 1 commit intomainfrom
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The rendered spec for this PR is available as a single page at https://tc39.es/ecma262/pr/3776 and as multiple pages at https://tc39.es/ecma262/pr/3776/multipage . |
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In #2007 we discussed the issue of counters and IIRC agreed that we should specify them as mathematical values with the understanding that implementations would diverge in the same way they diverge from the requirements to have arbitrarily large strings and callstacks and similar. I think that's better than this. |
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Even JSSE, the entirely AI-generated engine, gets this wrong: https://github.com/pmatos/jsse/blob/main/src/interpreter/builtins/iterators.rs. I guess it didn't read the spec... |
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All known engines are currently non-compliant. If they use Numbers as counters today, they'll stop advancing at 253. So counters passed to user-provided callbacks will always be 253 once they reach that point and take/drop will behave as if Infinity was passed. With this change, internal counters are now Numbers, so the argument passed to user-provided callbacks is expected to repeat at 253 (matching implementations today). In addition, take/drop throw a RangeError on finite inputs ≥ 253.
See tc39/proposal-iterator-includes#12 for context.