Converts a union type to an intersection type: A | B | C → A & B & C.
Uses conditional-type distribution and the contravariant position of a
function parameter to collapse the union into an intersection.
Available since v3.0.0
import type { UnionToIntersection } from '@helpers4/type';
// or, from the all-in-one package (same code, one install):
import type { UnionToIntersection } from 'helpers4/type';
type UnionToIntersection<U> =
(U extends unknown ? (x: U) => void : never) extends (x: infer I) => void ? I : never
type Union = { a: number } | { b: string } | { c: boolean };
type Intersection = UnionToIntersection<Union>;
// { a: number } & { b: string } & { c: boolean }
type Keys = UnionToIntersection<'a' | 'b'>;
// 'a' & 'b' (resolves to never for disjoint literals)
View source on GitHub
