rambdax/_ts-toolbelt/src/Any/IsLiteral.ts

Extended version of Rambda - a lightweight, faster alternative to Ramda

import {And} from '../Boolean/And'
import {Or} from '../Boolean/Or'
import {Extends} from './Extends'

/**
 * @hidden
 */
export type IsStringLiteral<A extends any> =
    A extends string
    ? string extends A
      ? 0
      : 1
    : 0

/**
 * @hidden
 */
export type IsNumberLiteral<A extends any> =
    A extends number
    ? number extends A
      ? 0
      : 1
    : 0

/**
 * Literal to restrict against
 */
export type Kind = string | number

/**
 * Determine whether `A` is literal or not
 * @param A to be checked
 * @param kind (?=`'string' | 'number'`) to restrict
 * @example
 * ```ts
 * import {A} from 'ts-toolbelt'
 *
 * type test0 = A.IsLiteral<1 | 2> // 1
 * type test1 = A.IsLiteral<1 | 2, string> // 0
 * type test2 = A.IsLiteral<1 | '2', string> // 0 | 1
 * type test3 = A.IsLiteral<number> // 0
 * ```
 */
export type IsLiteral<A extends any, kind extends Kind = Kind> =
    And<Or<IsStringLiteral<A>, IsNumberLiteral<A>>, Extends<A, kind>>