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Refer: Medium - Length of String

Describe

Compute the length of a string literal, which behaves like String#length.

Test Cases

code snippetCopytypescript
import { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<LengthOfString<''>, 0>>,
  Expect<Equal<LengthOfString<'kumiko'>, 6>>,
  Expect<Equal<LengthOfString<'reina'>, 5>>,
  Expect<Equal<LengthOfString<'Sound! Euphonium'>, 16>>,
]

Solution

code snippetCopytypescript
type LengthOfString<S extends string, C extends any[] = []> = S extends `${infer P}${infer K}`
  ? LengthOfString<K, [...C, P]>
  : C['length']