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Commit e4ca4ce

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philipp-spiessleebyron
philipp-spiess
authored and
leebyron
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Stop the iteration of an exhausted, unknown-sized sequence when slicing (#1324)
This PR fixes a bug with the slice operator that caused non value iterators of an unknown sized sequence to continue although the source sequence was exhausted, eventually accessing the value of a key/value pair that does not exist. The issue did not happen with fixed sized sequences since we can calculate resulting size in advance (as `sliceSize`) and bail out early. For an unknown sized sequence however, we can not know this size in advance (see this comment: [1]). To solve this, we now bail out when we encounter a completed iterator before proceeding to process it further. [1]: https://github.com/facebook/immutable-js/blob/27b231c8952366ddb96ab2a20d1eb351b3c8719e/src/Operations.js#L427-L428
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‎__tests__/slice.ts

Copy file name to clipboardExpand all lines: __tests__/slice.ts
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@@ -126,6 +126,28 @@ describe('slice', () => {
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expect(iterTail.next()).toEqual({value: undefined, done: true});
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});
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it('stops the entries iterator when the sequence has an undefined end', () => {
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let seq = Seq([0, 1, 2, 3, 4, 5]);
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// flatMap is lazy and thus the resulting sequence has no size.
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seq = seq.flatMap(a => [a]);
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expect(seq.size).toEqual(undefined);
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let iterFront = seq.slice(0, 2).entries();
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expect(iterFront.next()).toEqual({value: [0, 0], done: false});
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expect(iterFront.next()).toEqual({value: [1, 1], done: false});
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expect(iterFront.next()).toEqual({value: undefined, done: true});
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let iterMiddle = seq.slice(2, 4).entries();
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expect(iterMiddle.next()).toEqual({value: [0, 2], done: false});
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expect(iterMiddle.next()).toEqual({value: [1, 3], done: false});
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expect(iterMiddle.next()).toEqual({value: undefined, done: true});
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let iterTail = seq.slice(4, 123456).entries();
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expect(iterTail.next()).toEqual({value: [0, 4], done: false});
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expect(iterTail.next()).toEqual({value: [1, 5], done: false});
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expect(iterTail.next()).toEqual({value: undefined, done: true});
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});
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check.it('works like Array.prototype.slice',
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[gen.int, gen.array(gen.oneOf([gen.int, gen.undefined]), 0, 3)],
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(valuesLen, args) => {

‎dist/immutable.es.js

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+1-1Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1505,7 +1505,7 @@ function sliceFactory(collection, begin, end, useKeys) {
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return iteratorDone();
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}
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var step = iterator.next();
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if (useKeys || type === ITERATE_VALUES) {
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if (useKeys || type === ITERATE_VALUES || step.done) {
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return step;
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}
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if (type === ITERATE_KEYS) {

‎dist/immutable.js

Copy file name to clipboardExpand all lines: dist/immutable.js
+1-1Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1511,7 +1511,7 @@ function sliceFactory(collection, begin, end, useKeys) {
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return iteratorDone();
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}
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var step = iterator.next();
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if (useKeys || type === ITERATE_VALUES) {
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if (useKeys || type === ITERATE_VALUES || step.done) {
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return step;
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}
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if (type === ITERATE_KEYS) {

‎dist/immutable.min.js

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+1-1Lines changed: 1 addition & 1 deletion
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‎src/Operations.js

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+1-1Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -479,7 +479,7 @@ export function sliceFactory(collection, begin, end, useKeys) {
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return iteratorDone();
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}
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const step = iterator.next();
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if (useKeys || type === ITERATE_VALUES) {
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if (useKeys || type === ITERATE_VALUES || step.done) {
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return step;
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}
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if (type === ITERATE_KEYS) {

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