Implement the JavaScript Array.slice function in the type system. Slice<Arr, Start, End> takes the three argument. The output should be a subarray of Arr from index Start to End. Indexes with negative numbers should be counted from reversely.
For example
type Arr = [1, 2, 3, 4, 5]
type Result = Slice<Arr, 2, 4> // expected to be [3, 4]
/* _____________ Your Code Here _____________ */
type SliceLeft<Arr extends readonly any[], Start, isNegStart, PrevArr extends readonly any[] = []> =
(isNegStart extends true ? Arr['length'] : PrevArr['length']) extends Start ? Arr
: Arr extends [infer TFirst, ...infer TRest] ? SliceLeft<TRest, Start, isNegStart, [...PrevArr, TFirst]>
: [];
type SliceLeftIgnoreSign<Arr extends readonly any[], Start extends number> =
`${Start}` extends `-${infer PosStart extends number}` ? SliceLeft<Arr, PosStart, true> : SliceLeft<Arr, Start, false>;
type SliceRight<Arr extends readonly any[], End extends number, isNegEnd, PrevArr extends readonly any[] = []> =
(isNegEnd extends true ? PrevArr['length'] : Arr['length']) extends End ? Arr
: Arr extends [...infer TRest, infer TLast] ? SliceRight<TRest, End, isNegEnd, [TLast, ...PrevArr]>
: [];
type SliceRightIgnoreSign<Arr extends readonly any[], End extends number> =
`${End}` extends `-${infer PosEnd extends number}` ? SliceRight<Arr, PosEnd, true> : SliceRight<Arr, End, false>;
type Slice<Arr extends readonly any[], Start extends number = 0, End extends number = Arr['length']> =
`${Start}` extends `-${string}` ? SliceRightIgnoreSign<SliceLeftIgnoreSign<Arr, Start>, End>
: SliceLeftIgnoreSign<SliceRightIgnoreSign<Arr, End>, Start>
/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'
type Arr = [1, 2, 3, 4, 5]
type cases = [
// basic
Expect<Equal<Slice<Arr, 0, 1>, [1]>>,
Expect<Equal<Slice<Arr, 0, 0>, []>>,
Expect<Equal<Slice<Arr, 2, 4>, [3, 4]>>,
// optional args
Expect<Equal<Slice<[]>, []>>,
Expect<Equal<Slice<Arr>, Arr>>,
Expect<Equal<Slice<Arr, 0>, Arr>>,
Expect<Equal<Slice<Arr, 2>, [3, 4, 5]>>,
// negative index
Expect<Equal<Slice<Arr, 0, -1>, [1, 2, 3, 4]>>,
Expect<Equal<Slice<Arr, -3, -1>, [3, 4]>>,
// invalid
Expect<Equal<Slice<Arr, 10>, []>>,
Expect<Equal<Slice<Arr, 1, 0>, []>>,
Expect<Equal<Slice<Arr, 10, 20>, []>>,
]标签：Arr,Typescript,Slice,extends,Expect,139,type,infer From： https://www.cnblogs.com/Answer1215/p/16987515.html