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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Key for rest Tuple argument missing when mapping tuple type","articleBody":"### 🔎 Search Terms\n\n\"tuple\", \"tuple type\"\n\n### 🕗 Version \u0026 Regression Information\n\n- This changed between versions 5.3.3 and 5.4.2\n\n### ⏯ Playground Link\n\nhttps://www.typescriptlang.org/play?ts=5.4.2#code/C4TwDgpgBA4hwBUCuYA2EDSEQGcA8ya0EAHsBAHYAmOUSFA1hQPYDuFA2gLoB8UAvFADeHDFACWFKA2zMAZlELouALigYAvhxkh5ilMoDcAKGMB6M1ACSUgKwA6ACz2ATFFbQA5vCgADCkgAtgBGEABOUAA+UABEAAwxvuaWNlAOAMz26e5ePv5BoRHR8TFRsQCMicZCoJBQ5DjAArDwSpjY+ByNYZKeADRQ9kMBIeHcvBrJUNNQAHoA-KYW1nZOrjlQ3k2+JWVuxZW+UAAUrAAW4gDGZxK0EACOSOIAbgCG6BRNrxQgrK+4AEopqkMlkNls-LsDqVoi4kjVwNAGk1BHBEAZ2rg8F1gD0KP0oCNChMpjMFsYgA\n\n### 💻 Code\n\n```ts\r\ntype GetTupleKeys\u003cTuple extends unknown[]\u003e = {[K in keyof Tuple]: K}[keyof Tuple];\r\n\r\n// In 5.4.2 we get `number | \"0\"`\r\n// In 5.3.3 we get `number | \"0\" | \"1\"`\r\n{type test = GetTupleKeys\u003c[string, ...number[]]\u003e}\r\n//    ^?\r\n\r\n// In 5.4.2 we get `\"0\" | 2 | \"1\"` (which is equivalent anyways)\r\n// In 5.3.3 we get `\"0\" | \"1\" | 2`\r\n{type test = GetTupleKeys\u003c[string, number]\u003e}\r\n//    ^?\r\n```\r\n\n\n### 🙁 Actual behavior\n\nIn 5.4.2, rest arguments in tuples no longer get a dedicated key/index when mapping the tuple type. In the above example, the tuple type `[string, ...number[]]` effectively produces the keys `number | \"0\"`\n\n### 🙂 Expected behavior\n\nNo regression. The above example should be as 5.3.3 and resolve to the keys `number | \"0\" | \"1\"`\n\n### Additional information about the issue\n\nThis is specifically impacting the following code:\r\nhttps://github.com/sindresorhus/type-fest/blob/main/source/set-parameter-type.d.ts#L7\r\n\r\nAs reported in:\r\nhttps://github.com/sindresorhus/type-fest/issues/831","author":{"url":"https://github.com/trevorade","@type":"Person","name":"trevorade"},"datePublished":"2024-03-13T23:04:27.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/57770/TypeScript/issues/57770"}