Eojin Han

참고 : https://stackoverflow.com/questions/39494689/is-it-possible-to-restrict-number-to-a-certain-range

TS 4.1 - Recursive Conditional Type

TS 4.5 - Tail-Recursion Elimination on Conditional Types

이 둘을 조합하여 range sequence number union type을 생성하도록 타입을 정의할 수 있다.


type Ran<T extends number> = number extends T ? number :_Range<T, []>;
type _Range<T extends number, R extends unknown[]> = R['length'] extends T ? R[number] : _Range<T, [R['length'], ...R]>;

type R5 = Ran<998>
const a: R5 = 3 // correct
const b: R5 = 999 // wrong

https://stackoverflow.com/a/39495173 ← 여기 답변 게 더 좋음


type Enumerate<N extends number, Acc extends number[] = []> = Acc['length'] extends N
  ? Acc[number]
  : Enumerate<N, [...Acc, Acc['length']]>

type IntRange<F extends number, T extends number> = Exclude<Enumerate<T>, Enumerate<F>>

type T = IntRange<20, 300>

range union type 얻기