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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Allow use of spread operator in tuple types","articleBody":"## Search Terms\r\n\r\ntuple type rest spread typescript\r\n\r\n## Suggestion\r\n\r\nI'd like to be able to write tuple types using the spread operator. For example:\r\n\r\n```typescript\r\ntype Foo = [string, ...number[]]; // first elt must be string, rest must be numbers\r\n```\r\n\r\nCurrently, this produces an error at the ellipsis: \"Type expected\".\r\n\r\nHere is a question asking much the same thing on Stack Overflow: https://stackoverflow.com/questions/44934541/how-to-use-the-spread-operator-in-a-typescript-tuple\r\n\r\nIt seems related to https://github.com/Microsoft/TypeScript/issues/10727, but that issue focuses on Object rest/spread, whereas this is specifically about tuples.\r\n\r\n## Use Cases\r\n\r\nTyped tuples are part of the existing language. So it seems natural that one should be able to type rest arguments . \r\n\r\nFor example, if you want to represent a syntax tree, you might want to write:\r\n\r\n```typescript\r\ntype FunCall = ['FUNCALL', Symbol, ...Expression[]]; // error in 2.9.1 :(\r\ntype Symbol = string;\r\ntype Expression = FunCall | Scalar;\r\ntype Scalar = number | string | null;\r\n```\r\n\r\nBut this isn't allowed in Typescript 2.9.1.\r\n\r\n## Examples\r\n\r\n```typescript\r\ntype Foo = [string, ...number[]];\r\nconst f1: Foo = [\"str\", 2, 3, 4]; // should pass\r\nconst f2: Foo = [\"str\", \"2\", 3, 4]; // should fail: \r\n\t\t// \"Type '(string | number)[]' is not assignable to type 'number[]'.\r\nconst f2: Foo = [\"str\", 2, \"3\", 4]; // should fail:\r\n\t\t// \"Type '(number | string)[]' is not assignable to type 'number[]'.\r\nconst f1: Foo = [1, 2, 3, 4]; // should fail:\r\n\t\t// \"Type 'number' is not assignable to type 'string'.\r\n```\r\n## Checklist\r\n\r\nMy suggestion meets these guidelines:\r\n* [x] This wouldn't be a breaking change in existing TypeScript / JavaScript code\r\n* [x] This wouldn't change the runtime behavior of existing JavaScript code\r\n* [x] This could be implemented without emitting different JS based on the types of the expressions\r\n* [x] This isn't a runtime feature (e.g. new expression-level syntax)\r\n\r\n","author":{"url":"https://github.com/aneilbaboo","@type":"Person","name":"aneilbaboo"},"datePublished":"2018-06-12T13:44:30.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/24902/TypeScript/issues/24902"}