30970-shitariteraru.ts

/**
 * 30970 - IsFixedStringLiteralType
 *
 * Sometimes you may want to determine whether a string literal is a definite type. For example, when you want to check whether the type specified as a class identifier is a fixed string literal type.
 *
 * ```typescript
 * type Action<ID extends string> = { readonly id: ID };
 * ```
 *
 * Since it must be fixed, the following types must be determined as false.
 *
 * * never type
 * * Union of string literal types
 * * Template literal types with embedded string, number, bigint, boolean
 *
 * Determine whether the given type S is a definite string literal type.
 *
 *
 */

/* _____________ Your Code Here _____________ */

type IsNever<T> = [T] extends [never] ? true : false;

type IsUnion<A, U = A> = IsNever<A> extends true
  ? false
  : A extends unknown
    ? [U] extends [A]
      ? false
      : true
    : never;

type IsEmbedded<T> = string extends T
  ? true
  : `${bigint}` extends T
    ? true
    : `${number}` extends T
      ? true
      : `${boolean}` extends T
        ? true
        : `${(string & {})}` extends T
          ? true
          : false;

type IsFixedStringLiteralType<S extends string> = IsNever<S> extends true
  ? false
  : IsUnion<S> extends true
    ? false
    : S extends `${infer A}${infer Rest extends string}`
      ? IsEmbedded<A> extends true
        ? false
        : Rest extends ''
          ? true
          : IsFixedStringLiteralType<Rest>
      : false

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type testcase =
  | Expect<Equal<IsFixedStringLiteralType<'ABC'>, true>>
  | Expect<Equal<IsFixedStringLiteralType<string>, false>>
  | Expect<Equal<IsFixedStringLiteralType<'ABC' | 'DEF'>, false>>
  | Expect<Equal<IsFixedStringLiteralType<never>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${string}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${string & {}}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${number}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${bigint}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${boolean}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${true}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${false}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${null}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${undefined}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string & {}}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${number}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${bigint}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${boolean}`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${true}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${false}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${null}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${undefined}`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${string}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${string & {}}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${number}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${bigint}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${boolean}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`${true}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${false}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${null}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`${undefined}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${string & {}}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${number}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${bigint}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${boolean}DEF`>, false>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${true}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${false}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${null}DEF`>, true>>
  | Expect<Equal<IsFixedStringLiteralType<`ABC${undefined}DEF`>, true>>
  | true