4518 - Fill

4518 - Fill

by キリサメ qianxi (@qianxi0410) #中等 #tuple

题目

Fill, a common JavaScript function, now let us implement it with types.
Fill<T, N, Start?, End?>, as you can see,Fill accepts four types of parameters, of which T and N are required parameters, and Start and End are optional parameters.
The requirements for these parameters are: T must be a tuple, N can be any type of value, Start and End must be integers greater than or equal to 0.

type exp = Fill<[1, 2, 3], 0> // expected to be [0, 0, 0]

In order to simulate the real function, the test may contain some boundary conditions, I hope you can enjoy it 😃

在 Github 上查看：https://tsch.js.org/4518/zh-CN

代码

/* _____________ 你的代码 _____________ */

type Fill<
  T extends unknown[],
  N,
  Start extends number = 0,
  End extends number = T['length'],
  Count extends any[] = [],
  Flag extends boolean = Count['length'] extends Start ? true : false,
> = Count['length'] extends End
  ? T
  : T extends [infer F, ...infer Rest]
    ? Flag extends false
      ? [F, ...Fill<Rest, N, Start, End, [...Count, 0]>]
      : [N, ...Fill<Rest, N, Start, End, [...Count, 0], Flag>]
    : T

测试用例

/* _____________ 测试用例 _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Fill<[], 0>, []>>,
  Expect<Equal<Fill<[], 0, 0, 3>, []>>,
  Expect<Equal<Fill<[1, 2, 3], 0, 0, 0>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], 0, 2, 2>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], 0>, [0, 0, 0]>>,
  Expect<Equal<Fill<[1, 2, 3], true>, [true, true, true]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 0, 1>, [true, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 1, 3>, [1, true, true]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 10, 0>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 10, 20>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 0, 10>, [true, true, true]>>,
]

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