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Tuple type #50838
Description
The Tuple type
We want to create a type called Strings50 that is a tuple with 50 strings.
type Strings50 = [
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string,
string
];Welp, that's one way of doing it. Or, you could use this utility type I'm proposing:
type Tuple<T, N, R extends T[] = []> = R['length'] extends N ? R : Tuple<T, N, [...R, T]>;With this recursive type, the abomination above can be refactored to this:
type Strings50 = Tuple<string, 50>;Use case example
We have a function that takes in an array and a chunk size, then returns that same array chunked out:
const chunkArray = <T extends unknown>(arr: T[], size: number) => {
const copy = [...arr];
return [...Array(Math.ceil(arr.length / size))].map(() => copy.splice(0, size));
};
// x looks like -> [['hello', 'world'], ['foo', 'bar'], ['fizz', 'buzz']];
const x = chunkArray(['hello', 'world', 'foo', 'bar', 'fizz', 'buzz'], 2);This is fine. The function returns T[][], and x is a string[][]. But, since for our use case, we intend to use non-dynamic chunk sizes when calling this function, we can make the return type more accurate:
const chunkArray = <T extends unknown, N extends number>(arr: T[], size: N) => {
const copy = [...arr];
return [...Array(Math.ceil(arr.length / size))].map(() => copy.splice(0, size)) as Tuple<T, N>[];
};
const x = chunkArray(['hello', 'world', 'foo', 'bar', 'fizz', 'buzz'], 2);
const y = chunkArray(['hello', 'world', 'foo', 'bar', 'fizz', 'buzz'], 3);Instead of having the type string[][], x now has a type of [string, string][], and y of course has a type of [string, string, string][].
Activity
MartinJohns commentedon Sep 18, 2022
See #39522 (comment):
Related: #47874
Repeat to Tuple, 설명 참조