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fixes #229: flatMap supports returning both iterables and iterators #233

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merged 8 commits into from Oct 19, 2022
Merged

fixes #229: flatMap supports returning both iterables and iterators #233

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cd906f0
fixes #229: flatMap supports returning both iterables and iterators
michaelficarra Sep 9, 2022
7f36844
only CreateAsyncFromSyncIterator when necessary
michaelficarra Sep 13, 2022
57725e3
update
michaelficarra Sep 23, 2022
a808e48
accidentally dropped the fast path
michaelficarra Sep 23, 2022
267fa97
fix editorial issues
michaelficarra Sep 23, 2022
938a6a0
oops, async
michaelficarra Sep 26, 2022
390def7
Merge branch 'main' into GH-229
michaelficarra Sep 26, 2022
c94e37a
Merge branch 'main' into GH-229
michaelficarra Oct 19, 2022
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68 changes: 43 additions & 25 deletions spec.html
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Expand Up @@ -248,6 +248,39 @@ <h1>
1. Return _iteratorRecord_.
</emu-alg>
</emu-clause>

<emu-clause id="sec-getiteratorflattenable" type="abstract operation">
<h1>
GetIteratorFlattenable (
_obj_: an ECMAScript language value,
_hint_: ~sync~ or ~async~,
): either a normal completion containing an Iterator Record or a throw completion
</h1>
<dl class="header">
</dl>
<emu-alg>
1. If _obj_ is not an Object, throw a *TypeError* exception.
1. Let _alreadyAsync_ be *false*.
1. Let _method_ be *undefined*.
1. If _hint_ is ~async~, then
1. Set _method_ to ? Get(_obj_, @@asyncIterator).
1. Set _alreadyAsync_ to *true*.
1. If IsCallable(_method_) is *false*, then
1. Set _method_ to ? Get(_obj_, @@iterator).
1. Set _alreadyAsync_ to *false*.
1. If IsCallable(_method_) is *false*, then
1. Let _iterator_ be _obj_.
1. Set _alreadyAsync_ to *true*.
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i think this variable name is confusing, since _iterator_ isn't already async here, it just shouldn't be made async later (if i'm understanding right)

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This is only applicable in the _hint_ is ~async~ path. The iterator is assumed to be async if we're trying to get an async iterator. I could have guarded this assignment for clarity, but it wouldn't change the result.

1. Else,
1. Let _iterator_ be ? Call(_method_, _obj_).
1. Let _nextMethod_ be ? GetV(_iterator_, *"next"*).
1. If IsCallable(_nextMethod_) is *false*, throw a *TypeError* exception.
1. Let _iteratorRecord_ be the Iterator Record { [[Iterator]]: _iterator_, [[NextMethod]]: _nextMethod_, [[Done]]: *false* }.
1. If _hint_ is ~async~ and _alreadyAsync_ is *false*, then
1. Return CreateAsyncFromSyncIterator(_iteratorRecord_).
1. Return _iteratorRecord_.
</emu-alg>
</emu-clause>
</emu-clause>
</emu-clause>

Expand Down Expand Up @@ -310,14 +343,10 @@ <h1>Iterator.prototype</h1>
<emu-clause id="sec-iterator.from">
<h1>Iterator.from ( _O_ )</h1>
<emu-alg>
1. Let _usingIterator_ be ? GetMethod(_O_, @@iterator).
1. If _usingIterator_ is not *undefined*, then
1. Let _iteratorRecord_ be ? GetIterator(_O_, ~sync~, _usingIterator_).
1. If IsCallable(_iteratorRecord_.[[NextMethod]]) is *false*, throw a *TypeError* exception.
1. Let _hasInstance_ be ? OrdinaryHasInstance(%Iterator%, _iteratorRecord_.[[Iterator]]).
1. If _hasInstance_ is *true*, then
1. Return _iteratorRecord_.[[Iterator]].
1. Else, Let _iteratorRecord_ be ? GetIteratorDirect(_O_).
1. Let _iteratorRecord_ be ? GetIteratorFlattenable(_O_, ~sync~).
1. Let _hasInstance_ be ? OrdinaryHasInstance(%Iterator%, _iteratorRecord_.[[Iterator]]).
1. If _hasInstance_ is *true*, then
1. Return _iteratorRecord_.[[Iterator]].
1. Let _wrapper_ be OrdinaryObjectCreate(%WrapForValidIteratorPrototype%, « [[Iterated]] »).
1. Set _wrapper_.[[Iterated]] to _iteratorRecord_.
1. Return _wrapper_.
Expand Down Expand Up @@ -392,21 +421,10 @@ <h1>AsyncIterator.prototype</h1>
<emu-clause id="sec-asynciterator.from">
<h1>AsyncIterator.from ( _O_ )</h1>
<emu-alg>
1. Let _usingIterator_ be ? GetMethod(_O_, @@asyncIterator).
1. Let _iteratorRecord_ be *undefined*.
1. If _usingIterator_ is not *undefined*, then
1. Set _iteratorRecord_ to ? GetIterator(_O_, ~async~, _usingIterator_).
1. If IsCallable(_iteratorRecord_.[[NextMethod]]) is *false*, throw a *TypeError* exception.
1. Let _hasInstance_ be ? OrdinaryHasInstance(%AsyncIterator%, _iteratorRecord_.[[Iterator]]).
1. If _hasInstance_ is *true*, then
1. Return _iteratorRecord_.[[Iterator]].
1. If _iteratorRecord_ is *undefined*, then
1. Set _usingIterator_ to ? GetMethod(_O_, @@iterator).
1. If _usingIterator_ is not *undefined*, then
1. Let _syncIteratorRecord_ be ? GetIterator(_O_, ~sync~, _usingIterator_).
1. If IsCallable(_syncIteratorRecord_.[[NextMethod]]) is *false*, throw a *TypeError* exception.
1. Set _iteratorRecord_ to CreateAsyncFromSyncIterator(_syncIteratorRecord_).
1. If _iteratorRecord_ is *undefined*, set _iteratorRecord_ to ? GetIteratorDirect(_O_).
1. Let _iteratorRecord_ be ? GetIteratorFlattenable(_O_, ~async~).
1. Let _hasInstance_ be ? OrdinaryHasInstance(%AsyncIterator%, _iteratorRecord_.[[Iterator]]).
1. If _hasInstance_ is *true*, then
1. Return _iteratorRecord_.[[Iterator]].
1. Let _wrapper_ be OrdinaryObjectCreate(%WrapForValidAsyncIteratorPrototype%, « [[AsyncIterated]] »).
1. Set _wrapper_.[[AsyncIterated]] to _iteratorRecord_.
1. Return _wrapper_.
Expand Down Expand Up @@ -651,7 +669,7 @@ <h1>Iterator.prototype.flatMap ( _mapper_ )</h1>
1. Let _value_ be ? IteratorValue(_next_).
1. Let _mapped_ be Completion(Call(_mapper_, *undefined*, « _value_, 𝔽(_counter_) »)).
1. IfAbruptCloseIterator(_mapped_, _iterated_).
1. Let _innerIterator_ be Completion(GetIterator(_mapped_, ~sync~)).
1. Let _innerIterator_ be Completion(GetIteratorFlattenable(_mapped_, ~sync~)).
1. IfAbruptCloseIterator(_innerIterator_, _iterated_).
1. Let _innerAlive_ be *true*.
1. Repeat, while _innerAlive_ is *true*,
Expand Down Expand Up @@ -928,7 +946,7 @@ <h1>AsyncIterator.prototype.flatMap ( _mapper_ )</h1>
1. IfAbruptCloseAsyncIterator(_mapped_, _iterated_).
1. Set _mapped_ to Completion(Await(_mapped_)).
1. IfAbruptCloseAsyncIterator(_mapped_, _iterated_).
1. Let _innerIterator_ be Completion(GetIterator(_mapped_, ~async~)).
1. Let _innerIterator_ be Completion(GetIteratorFlattenable(_mapped_, ~async~)).
1. IfAbruptCloseAsyncIterator(_innerIterator_, _iterated_).
1. Let _innerAlive_ be *true*.
1. Repeat, while _innerAlive_ is *true*,
Expand Down