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Try to fix issue with empty list that is a singleton #2004

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Merged
merged 4 commits into from
Oct 17, 2024
Merged

Try to fix issue with empty list that is a singleton #2004

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2ec55e6
Try to fix issue with empty list that is a singleton
jdeniau Jul 22, 2024
d410932
Update List.ts
jdeniau Jul 22, 2024
8997771
Freeze emptyList to avoid mutation
jdeniau Sep 24, 2024
14631a6
Do not keep a singletin of EMPTY_LIST
jdeniau Sep 24, 2024
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33 changes: 32 additions & 1 deletion __tests__/List.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -829,7 +829,7 @@ describe('List', () => {
it('chained mutations does not result in new empty list instance', () => {
const v1 = List(['x']);
const v2 = v1.withMutations(v => v.push('y').pop().pop());
expect(v2).toBe(List());
expect(v2).toEqual(List());
});

it('calling `clear` and `setSize` should set all items to undefined', () => {
Expand Down Expand Up @@ -927,6 +927,37 @@ describe('List', () => {
expect(isNaNValue(list.get(0))).toBe(true);
});

it('return a new emptyList if the emptyList has been mutated #2003', () => {
const emptyList = List();

const nonEmptyList = emptyList.withMutations(l => {
l.setSize(1);
l.set(0, 'a');
});

expect(nonEmptyList.size).toBe(1);
expect(nonEmptyList).toEqual(List.of('a'));
expect(emptyList.size).toBe(0);

const mutableList = emptyList.asMutable();

mutableList.setSize(1);
mutableList.set(0, 'b');

expect(mutableList.size).toBe(1);
expect(mutableList).toEqual(List.of('b'));

expect(emptyList.size).toBe(0);
expect(List().size).toBe(0);
});

it('Mutating empty list with a JS API should not mutate new instances', () => {
Object.assign(List(), List([1, 2]));

expect(List().size).toBe(0);
expect(List().toArray()).toEqual([]);
});

// Note: NaN is the only value not equal to itself. The isNaN() built-in
// function returns true for any non-numeric value, not just the NaN value.
function isNaNValue(value) {
Expand Down
3 changes: 1 addition & 2 deletions src/List.js
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Original file line number Diff line number Diff line change
Expand Up @@ -408,9 +408,8 @@ function makeList(origin, capacity, level, root, tail, ownerID, hash) {
return list;
}

let EMPTY_LIST;
export function emptyList() {
return EMPTY_LIST || (EMPTY_LIST = makeList(0, 0, SHIFT));
return makeList(0, 0, SHIFT);
}

function updateList(list, index, value) {
Expand Down