Type Alias UnionToOverloadedFn<U>

UnionToOverloadedFn: (U extends any ? (k: U) => void : never) extends (
    k: infer I,
) => void
    ? I
    : never

Convert a union to an overloaded function and extract tuple form. Note: this is an established trick but can be slow for very large unions.

type U = 'a' | 'b' | 'c';
type Fn = UnionToOverloadedFn<U>; // (k: 'a') => void & (k: 'b') => void & (k: 'c') => void