定义固定长度的数组

来源: https://stackoverflow.com/questions/52489261/typescript-can-i-define-an-n-length-tuple-type

Typescript 3 introduces rest elements in tuple types

The last element of a tuple type can be a rest element of the form ...X, where X is an array type

To restrict the length of a tuple we can use intersection with { length: N }

定义类型

type Tuple<TItem, TLength extends number> = [TItem, ...TItem[]] & { length: TLength };

那么定长为6的数组就是

let matrix: Tuple<number, 6>
matrix = [1,2,3,4,5,6]