「重学TS 2.0 」TS 练习题第三十七题

[semlinker]

实现一个 Flat 工具类型，支持把数组类型拍平（扁平化）。具体的使用示例如下所示：

type Flat<T extends any[]> = // 你的实现代码

type F0 = Flat<[]> // []
type F1 = Flat<['a', 'b', 'c']> // ["a", "b", "c"]
type F2 = Flat<['a', ['b', 'c'], ['d', ['e', ['f']]]]> // ["a", "b", "c", "d", "e", "f"]

请在下面评论你的答案

[zhaoxiongfei]

type Flat<T extends any[]> = T extends [infer First, ...infer Rest]
  ? First extends any[]
    ? [...Flat<First>, ...Flat<Rest>]
    : [First, ...Flat<Rest>]
  : [];

type F0 = Flat<[]>; // []
type F1 = Flat<["a", "b", "c"]>; // ["a", "b", "c"]
type F2 = Flat<["a", ["b", "c"], ["d", ["e", ["f"]]]]>; // ["a", "b", "c", "d", "e", "f"]

[mingzhans]

type Flat<T extends any[], S extends any[] = []> = T extends [infer R, ...infer Rest]?
  R extends any[] ?
  Flat<Rest, Flat<R, S>> : 
  Flat<Rest, [...S, R]> : 
  S// 你的实现代码
type F0 = Flat<[]>; // []
type F1 = Flat<["a", "b", "c"]>; // ["a", "b", "c"]
type F2 = Flat<["a", ["b", "c"], ["d", ["e", ["f"]]]]>; // ["a", "b", "c", "d", "e", "f"]

两层递归

[Cxdhz]

type Flat<T extends any[]> = 
    T extends [infer A, ...infer B] 
    ? [...(A extends any[] ? Flat<A> : [A]), ...Flat<B>] 
    : []

type F0 = Flat<[]> // []
type F1 = Flat<['a', 'b', 'c']> // ["a", "b", "c"]
type F2 = Flat<['a', ['b', 'c'], ['d', ['e', ['f']]]]> // ["a", "b", "c", "d", "e", "f"]

[jackwangwj]

type Flat<T extends any[]> =
T extends [infer A, ...infer Rest]
? A extends [...infer Rest2]
? [...Flat, ...Flat]
: [A, ...Flat]
: T
// 你的实现代码

type F0 = Flat<[]> // []
type F1 = Flat<['a', 'b', 'c']> // ["a", "b", "c"]
type F2 = Flat<['a', ['b', 'c'], ['d', ['e', ['f']]]]> // ["a", "b", "c", "d", "e", "f"]

[zjxxxxxxxxx]

type Flat<T extends any[]> = T extends [infer F, ...infer R]
  ? F extends any[]
    ? [...Flat<F>, ...Flat<R>]
    : [F, ...Flat<R>]
  : T;

[bill-lai]

type Flat<T extends any[]> = 
  T extends [infer P1, ...infer P2]
    ? [...(P1 extends any[] ? Flat<P1> : [P1]), ...Flat<P2>]
    : []

[dentm]

type Flat<T extends any[], U extends any[] = []> =
    T['length'] extends 0 
    ? U 
    : T extends [infer X, ...infer B] 
    ? (X extends [infer D, ...infer E] ? Flat<[...E, ...B], [...U, D]>  : Flat<B, [...U, X]> ) 
    : U

type F0 = Flat<[]> // []
type F1 = Flat<['a', 'b', 'c']> // ["a", "b", "c"]
type F2 = Flat<[
    'a', 
    ['b', 'c'], 
    ['d', ['e', ['f']]]
]> // ["a", "b", "c", "d", "e", "f"]