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Number Range

2022-04-27 08

题目来源(type-challenges)

问题

限制数字范围

type Result1 = | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
type Result2 = | 0 | 1 | 2
type Result3 =
  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10
  | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20
  | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30
  | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40
  | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50
  | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60
  | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70
  | 71 | 72 | 73 | 74 | 75 | 76 | 77 | 78 | 79 | 80
  | 81 | 82 | 83 | 84 | 85 | 86 | 87 | 88 | 89 | 90
  | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 | 100
  | 101 | 102 | 103 | 104 | 105 | 106 | 107 | 108 | 109 | 110
  | 111 | 112 | 113 | 114 | 115 | 116 | 117 | 118 | 119 | 120
  | 121 | 122 | 123 | 124 | 125 | 126 | 127 | 128 | 129 | 130
  | 131 | 132 | 133 | 134 | 135 | 136 | 137 | 138 | 139 | 140

type case1 = NumberRange<2, 9> //  Result1
type case2 = NumberRange<0, 2> //  Result2
type case3 = NumberRange<0, 140> //  Result3

解答 

type Arr<T, U extends 1[] = []> = U['length'] extends T ? U : Arr<T, [...U, 1]>;
type NumberRange<L, H, C extends 1[] = Arr<L>, R extends any = never> = C['length'] extends H ? R | C['length']: NumberRange<L, H, [...C, 1], R | C['length']>

拆分

  1. 默认从 L 长度开始叠加
  2. 直到叠加到 H 长度
  3. 多一个联合类型参数直接返回
cd ..