A non-recursive type-level inclusion operator
type E1<X> = <T>() => T extends X ? 0 : 1 type E2<X> = <T>() => T extends X ? 0 : 1 type IsEqual<X, Y> = E1<X> extends E2<Y> ? true : false /** * Whether or not T includes U as an element. */ type Includes<T extends readonly unknown[], U> = true extends { [key in keyof T]: IsEqual<T[key], U> }[number] ? true : false A non-recursive type-level Includes operator in Typescript Introduction Includes is a type-level operator that determines whether a given type T includes a given type U as an element.