UnionToIntersection

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) // The `& Union` is to ensure result of `UnionToIntersection<A | B>` is always assignable to `A | B` ? Intersection & Union : never

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) // The `& Union` is to ensure result of `UnionToIntersection<A | B>` is always assignable to `A | B` ? Intersection & Union : never