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Flatten

介绍​

在这个挑战中，你需要写一个接受数组的类型，并且返回扁平化的数组类型。

ts
type flatten = Flatten<[1, 2, [3, 4], [[[5]]]]> // [1, 2, 3, 4, 5]
ts
type flatten = Flatten<[1, 2, [3, 4], [[[5]]]]> // [1, 2, 3, 4, 5]
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type Flatten = any
 
/* _____________ Test Cases _____________ */
 
 
 
type cases = [
  Expect<Equal<Flatten<[]>, []>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[1, 2, 3, 4]>, [1, 2, 3, 4]>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[1, [2]]>, [1, 2]>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[1, 2, [3, 4], [[[5]]]]>, [1, 2, 3, 4, 5]>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[{ foo: 'bar', 2: 10 }, 'foobar']>, [{ foo: 'bar', 2: 10 }, 'foobar']>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
]
 
ts
/* _____________ Your Code Here _____________ */
 
type Flatten = any
 
/* _____________ Test Cases _____________ */
 
 
 
type cases = [
  Expect<Equal<Flatten<[]>, []>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[1, 2, 3, 4]>, [1, 2, 3, 4]>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[1, [2]]>, [1, 2]>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[1, 2, [3, 4], [[[5]]]]>, [1, 2, 3, 4, 5]>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
  Expect<Equal<Flatten<[{ foo: 'bar', 2: 10 }, 'foobar']>, [{ foo: 'bar', 2: 10 }, 'foobar']>>,
Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.2344
2315Type 'false' does not satisfy the constraint 'true'.
Type 'Flatten' is not generic.
]
 
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解决方案​

Spoiler warning // Click to reveal answer
ts
type Flatten<T extends any[]> = T extends [infer F, ...infer Rest] 
  ? F extends any[] 
    ? [...Flatten<F>, ...Flatten<Rest>]  
    : [F, ...Flatten<Rest>] 
  : T;
ts
type Flatten<T extends any[]> = T extends [infer F, ...infer Rest] 
  ? F extends any[] 
    ? [...Flatten<F>, ...Flatten<Rest>]  
    : [F, ...Flatten<Rest>] 
  : T;
ts
// most popular
 
type Flatten<S extends any[], T extends any[] = []> =  S extends [infer X, ...infer Y] ? 
  X extends any[] ?
   Flatten<[...X, ...Y], T> : Flatten<[...Y], [...T, X]> 
  : T;
 
 
ts
// most popular
 
type Flatten<S extends any[], T extends any[] = []> =  S extends [infer X, ...infer Y] ? 
  X extends any[] ?
   Flatten<[...X, ...Y], T> : Flatten<[...Y], [...T, X]> 
  : T;
 
 
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