Home > types > UnionToIntersection
Convert a union type to an intersection type using [distributive conditional types](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#distributive-conditional-types).
Inspired by [this Stack Overflow answer](https://stackoverflow.com/a/50375286/2172153).
Signature:
export declare type UnionToIntersection<Union> = (
// `extends unknown` is always going to be the case and is used to convert the
// `Union` into a [distributive conditional
// type](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html#distributive-conditional-types).
Union extends unknown
// The union type is used as the only argument to a function since the union
// of function arguments is an intersection.
? (distributedUnion: Union) => void
// This won't happen.
: never
// Infer the `Intersection` type since TypeScript represents the positional
// arguments of unions of functions as an intersection of the union.
) extends ((mergedIntersection: infer Intersection) => void)
? Intersection
: never;
```import {UnionToIntersection} from ‘type-fest’;
| type Union = {the(): void} | {great(arg: string): void} | {escape: boolean}; |
type Intersection = UnionToIntersection
A more applicable example which could make its way into your library code follows.
@example
``` import {UnionToIntersection} from ‘type-fest’;
class CommandOne { commands: { a1: () => undefined, b1: () => undefined, } }
class CommandTwo { commands: { a2: (argA: string) => undefined, b2: (argB: string) => undefined, } }
const union = [new CommandOne(), new CommandTwo()].map(instance => instance.commands); type Union = typeof union; //=> {a1(): void; b1(): void} | {a2(argA: string): void; b2(argB: string): void}
type Intersection = UnionToIntersection
Utilities