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MurkyMeow/range-extension.ts

Created February 9, 2021 00:32
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range-extension.ts
type NumberRange<N extends number, A extends number[] = []> =
A['length'] extends N ? A : NumberRange<N, [...A, A['length']]>
type Upto10 = NumberRange<10> // [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
// If TS is too lazy to unwind a deep recursion (depth = 46):
type Upto46_ = NumberRange<46> // Type instantiation is excessively deep and possibly infinite
// We can reduce it's depth by specifying a bigger initial array (now depth = 36):
type Upto46 = NumberRange<46, NumberRange<10>> // [0, 1, 2, 3, 4, ..., 45]
// So the range can be as big as you want
type Upto100 = NumberRange<100, NumberRange<55, NumberRange<45>>> // [0, 1, 2, 3, 4, ..., 99]
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range.ts
type ValuesOf<T> = T extends (infer R)[] ? R : never
type NumberRange<N extends number, A extends number[] = []> =
A['length'] extends N ? ValuesOf<A> : NumberRange<N, [...A, A['length']]>
type Upto10 = NumberRange<10> // 0 | 1 | 2 | 3 | 4 |5 | 6 | 7 | 8 | 9
type Between20And10 = Exclude<NumberRange<21>, NumberRange<10>> // 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20
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