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Join

介绍​

实现数组的join类型, Join<T,U>接收数组T, 字符串或数值U, 返回使用U链接的T

ts
type Res = Join<["a", "p", "p", "l", "e"], "-">; // expected to be 'a-p-p-l-e'
type Res1 = Join<["Hello", "World"], " ">; // expected to be 'Hello World'
type Res2 = Join<["2", "2", "2"], 1>; // expected to be '21212'
type Res3 = Join<["o"], "u">; // expected to be 'o'
ts
type Res = Join<["a", "p", "p", "l", "e"], "-">; // expected to be 'a-p-p-l-e'
type Res1 = Join<["Hello", "World"], " ">; // expected to be 'Hello World'
type Res2 = Join<["2", "2", "2"], 1>; // expected to be '21212'
type Res3 = Join<["o"], "u">; // expected to be 'o'
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起点​

ts
/* _____________ Your Code Here _____________ */
 
type Join<T, U> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<Join<['a', 'p', 'p', 'l', 'e'], '-'>, 'a-p-p-l-e'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['Hello', 'World'], ' '>, 'Hello World'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['2', '2', '2'], 1>, '21212'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['o'], 'u'>, 'o'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<[], 'u'>, ''>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['1', '1', '1']>, '1,1,1'>>,
Type 'false' does not satisfy the constraint 'true'.
Generic type 'Join' requires 2 type argument(s).2344
2314Type 'false' does not satisfy the constraint 'true'.
Generic type 'Join' requires 2 type argument(s).
]
ts
/* _____________ Your Code Here _____________ */
 
type Join<T, U> = any
 
/* _____________ Test Cases _____________ */
 
type cases = [
  Expect<Equal<Join<['a', 'p', 'p', 'l', 'e'], '-'>, 'a-p-p-l-e'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['Hello', 'World'], ' '>, 'Hello World'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['2', '2', '2'], 1>, '21212'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['o'], 'u'>, 'o'>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<[], 'u'>, ''>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.
  Expect<Equal<Join<['1', '1', '1']>, '1,1,1'>>,
Type 'false' does not satisfy the constraint 'true'.
Generic type 'Join' requires 2 type argument(s).2344
2314Type 'false' does not satisfy the constraint 'true'.
Generic type 'Join' requires 2 type argument(s).
]
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解决方案​

Spoiler warning // Click to reveal answer
ts
// most popular
 
type Join<T extends any[], U extends string | number> = T extends [infer F, ...infer R]
  ? R['length'] extends 0
    ? `${F & string}`
    : `${F & string}${U}${Join<R, U>}`
  : never
 
ts
// most popular
 
type Join<T extends any[], U extends string | number> = T extends [infer F, ...infer R]
  ? R['length'] extends 0
    ? `${F & string}`
    : `${F & string}${U}${Join<R, U>}`
  : never
 
ts
// my solution
 
type Join<T extends any[], U extends string|number=',', S extends string = ''> = T extends [infer F extends string|number, ...infer R]
  ? Join<R, U, `${S}${U}${F}`>
  : S extends `${infer F extends U}${infer R}`
    ? R
    : S;
 
ts
// my solution
 
type Join<T extends any[], U extends string|number=',', S extends string = ''> = T extends [infer F extends string|number, ...infer R]
  ? Join<R, U, `${S}${U}${F}`>
  : S extends `${infer F extends U}${infer R}`
    ? R
    : S;
 
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