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25747-hard-isnegativenumber
Hard
number
template literal

チャレンジのソース: type-challenges/25747-hard-isnegativenumber

Sometimes when working with numeric literals, we need to rule out (or enforce) that the provided number is a positive integer.

To do that, we first need a way to tell if the number is negative.

Write a type-level function IsNegativeNumber that accepts a number N and returns:

  • true if N is negative
  • false if N is positive
  • false if N is 0,
  • never if N is number
  • never if N is a union

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テストケースの出典: type-challenges/25747-hard-isnegativenumber/test-cases.ts
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<IsNegativeNumber<0>, false>>,
  Expect<Equal<IsNegativeNumber<number>, never>>,
  Expect<Equal<IsNegativeNumber<-1 | -2>, never>>,
  Expect<Equal<IsNegativeNumber<-1>, true>>,
  Expect<Equal<IsNegativeNumber<-1.9>, true>>,
  Expect<Equal<IsNegativeNumber<-100_000_000>, true>>,
  Expect<Equal<IsNegativeNumber<1>, false>>,
  Expect<Equal<IsNegativeNumber<1.9>, false>>,
  Expect<Equal<IsNegativeNumber<100_000_000>, false>>,
]