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Unshift

介绍​

实现Array.unshift类型版本

For example

typescript
type Result = Unshift<[1, 2], 0>; // [0, 1, 2,]
typescript
type Result = Unshift<[1, 2], 0>; // [0, 1, 2,]
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起点​

ts
/* _____________ Your Code Here _____________ */
type Unshift<T, U> = any;
 
/* _____________ Test Cases _____________ */
type cases = [
  Expect<Equal<Unshift<[], 1>, [1]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Unshift<[1, 2], 0>, [0, 1, 2]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Unshift<['1', 2, '3'], boolean>, [boolean, '1', 2, '3']>>
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
];
ts
/* _____________ Your Code Here _____________ */
type Unshift<T, U> = any;
 
/* _____________ Test Cases _____________ */
type cases = [
  Expect<Equal<Unshift<[], 1>, [1]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Unshift<[1, 2], 0>, [0, 1, 2]>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Unshift<['1', 2, '3'], boolean>, [boolean, '1', 2, '3']>>
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
];
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解决方案​

Spoiler warning // Click to reveal answer
ts
// 方案1
type Unshift<T,U> = T extends unknown[] ? [U, ...T] : never
ts
// 方案1
type Unshift<T,U> = T extends unknown[] ? [U, ...T] : never
ts
// 方案2
type Unshift<T, U> = T extends [...infer Rest] ? [U, ...Rest] : never;
ts
// 方案2
type Unshift<T, U> = T extends [...infer Rest] ? [U, ...Rest] : never;
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