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/**
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).
@example
```
import {UnionToIntersection} from 'type-fest';
type Union = {the(): void} | {great(arg: string): void} | {escape: boolean};
type Intersection = UnionToIntersection<Union>;
//=> {the(): void; great(arg: string): void; escape: boolean};
```
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<Union>;
//=> {a1(): void; b1(): void; a2(argA: string): void; b2(argB: string): void}
```
*/
export 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;
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