rambda/_ts-toolbelt/src/Object/ReadonlyKeys.ts

Lightweight faster alternative to Ramda

import {Keys} from './Keys'
import {Equals} from '../Any/Equals'

// Credit https://stackoverflow.com/a/52473108/3570903

/** Get the keys of **`O`** that are readonly
 * @param O
 * @returns **`keyof`**
 * @example
 * ```ts
 * ```
 */
export type ReadonlyKeys<O extends object> = {
    [K in keyof O]-?: {
        1: never
        0: K
    }[Equals<{-readonly [Q in K]: O[K]}, {[Q in K]: O[K]}>]
}[Keys<O>]