ultimateMatcher.ts

ultimateMatcher.ts

declare export function match<
  DiscriminatedUnion extends { [K in Discriminator]: string | number },
  Pattern extends Partial<
    {
      [K in DiscriminatedUnion[Discriminator]]: (
        v: Extract<DiscriminatedUnion, { kind: K }>
      ) => any;
    }
  >,
  Discriminator extends string | number = "kind"
>(
  input: DiscriminatedUnion,
  pattern: Exclude<
    keyof Pattern,
    DiscriminatedUnion[Discriminator]
  > extends never
    ? Pattern
    : Partial<
        {
          [K in DiscriminatedUnion[Discriminator]]: (
            v: Extract<DiscriminatedUnion, { kind: K }>
          ) => any;
        }
      >,
  discriminator?: Discriminator
): typeof pattern extends {
  [K in DiscriminatedUnion[Discriminator]]: (
    v: Extract<DiscriminatedUnion, { kind: K }>
  ) => infer Res;
}
  ? string extends DiscriminatedUnion[Discriminator]
    ? Res | undefined
    : unknown extends Res
    ? undefined
    : Res
  : typeof pattern extends Partial<
      {
        [K in DiscriminatedUnion[Discriminator]]: (
          v: Extract<DiscriminatedUnion, { kind: K }>
        ) => infer Res;
      }
    >
  ? Res | undefined
  : never;