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make Join work with const tuple values #533

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merged 1 commit into from Dec 25, 2022
Merged

make Join work with const tuple values #533

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4 changes: 2 additions & 2 deletions source/join.d.ts
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Expand Up @@ -21,13 +21,13 @@ const path: Join<[1, 2, 3], '.'> = [1, 2, 3].join('.');
@category Template literal
*/
export type Join<
Strings extends Array<string | number>,
Strings extends Readonly<Array<string | number>>,
Delimiter extends string,
> = Strings extends []
? ''
: Strings extends [string | number]
? `${Strings[0]}`
: Strings extends [
: Strings extends readonly [
string | number,
...infer Rest extends Array<string | number>,
]
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11 changes: 11 additions & 0 deletions test-d/join.ts
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Expand Up @@ -21,3 +21,14 @@ expectNotAssignable<'foo.bar.baz'>(emptyDelimiter);
const emptyInput: Join<[], '.'> = '';
expectType<''>(emptyInput);
expectNotAssignable<'foo'>(emptyInput);

// Typeof of const tuple
const tuple = ['foo', 'bar', 'baz'] as const;
const joinedTuple: Join<typeof tuple, ','> = 'foo,bar,baz';
expectType<'foo,bar,baz'>(joinedTuple);

// Typeof of string[]
const stringArray = ['foo', 'bar', 'baz'];
const joinedStringArray: Join<typeof stringArray, ','> = '';
expectType<string>(joinedStringArray);
expectNotAssignable<'foo,bar,baz'>(joinedStringArray);