[TS] type-challenges: 18. Length of Tuple

문제

배열(튜플)을 받아 길이를 반환하는 제네릭 Length<T>를 구현하세요.

 

type tesla = ['tesla', 'model 3', 'model X', 'model Y']
type spaceX = ['FALCON 9', 'FALCON HEAVY', 'DRAGON', 'STARSHIP', 'HUMAN SPACEFLIGHT']

type teslaLength = Length<tesla>  // expected 4
type spaceXLength = Length<spaceX> // expected 5

 

풀이

type Length<T extends any[]> = T['length'];

간단하게 이렇게 표현했더니

 

Type 'readonly ["tesla", "model 3", "model X", "model Y"]' does not satisfy the constraint 'any[]'.

이런게 떴다

 

type Length<T extends readonly any[]> = T['length'];

readonly를 제네릭에 붙여줬더니 성공

 

출처

https://github.com/type-challenges/type-challenges/blob/main/questions/00018-easy-tuple-length/README.ko.md

GitHub - type-challenges/type-challenges: Collection of TypeScript type challenges with online judge