Immutable-js Typescript 2.8 attempt

immutable-typescript-attempt.ts

import { Map, fromJS } from 'immutable'

function toImmutable<T>(array: T[]): ImmutableList<T>
function toImmutable<T extends object>(obj: T): ImmutableObject<T>
function toImmutable<T>(value: T): ImmutableObject<T> | ImmutableList<T> {
	return fromJS(value)
}

type Diff<T, U> = T extends U ? never : T

type ImmutableObjectValues<T> = {
	[P in keyof T]: 
		undefined extends T[P] ? (
			Diff<T[P], undefined> extends object ? undefined | ImmutableObject<Diff<T[P], undefined>> : 
			T[P]
		) :
		T[P] extends any[] ? ImmutableList<T[P][number]> :
		T[P] extends object ? ImmutableObject<T[P]> : T[P]
}

interface ImmutableObject<T> {
	get<P extends keyof T>(key: P): ImmutableObjectValues<T>[P]
	set<P extends keyof T>(key: P, value: ImmutableObjectValues<T>[P]): ImmutableObject<T>
	toObject(): T
}

function ImmutableList<T>(list: T): ImmutableList<T> {
	return fromJS(list)
}

interface ImmutableList<T> {
	count(): number
	get(index: number): T extends object ? ImmutableObject<T> : T
	toArray(): [T]
}

The big problem is that it doesn't currently support nested sets or any nested operations.