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replace concat with spread: items can be arrays #527

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merged 1 commit into from
Jan 2, 2023
Merged

replace concat with spread: items can be arrays #527

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2 changes: 1 addition & 1 deletion packages/array-permutations/index.cjs
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ function permutations(arr) {
for (var j = 0, len2 = partial.length; j <= len2; j++) {
var start = partial.slice(0, j);
var end = partial.slice(j);
var merged = start.concat(first, end);
var merged = start.concat([first], end);

output.push(merged);
}
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2 changes: 1 addition & 1 deletion packages/array-permutations/index.mjs
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Expand Up @@ -28,7 +28,7 @@ function permutations(arr) {
for (var j = 0, len2 = partial.length; j <= len2; j++) {
var start = partial.slice(0, j);
var end = partial.slice(j);
var merged = start.concat(first, end);
var merged = start.concat([first], end);
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"first" is an item of the array being permuted. So if arr has type T[], then:

arr: T[]
first: T
start: T[]
end: T[]

The arguments to concat should both be of type T[].

The fact that this was (mostly) working before is due to JS's concat behaving somewhat like push: it can accept non-array values. But if T itself is an array type, then this did not work as intended.


output.push(merged);
}
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4 changes: 3 additions & 1 deletion test/array-permutations/index.cjs
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Expand Up @@ -2,7 +2,7 @@ var test = require('../util/test')(__filename);
var permutations = require('../../packages/array-permutations');

test('array with all permutations', function(t) {
t.plan(4);
t.plan(5);

t.deepEqual(
permutations(['javascript', 'typescript']),
Expand All @@ -17,6 +17,8 @@ test('array with all permutations', function(t) {
t.deepEqual(permutations([]), []);
t.deepEqual(permutations([1]), [[1]]);

t.deepEqual(permutations([[1], [2]]), [[[1], [2]], [[2], [1]]]);

t.end();
});

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