Final merge latest from operator

merge latest from final.ts

export type ObservableSourceType<T = any> = Observable<T> | ((value: any) => Observable<T>);

function* sourcesGen<T>(sources: ObservableSourceType[], a: T, i: number): Generator<Observable<any>, Observable<any>, undefined> {
  const length = sources.length;
  for (const [index, source] of sources.entries()) {
    const observableSource: Observable<any> = typeof source === 'function' ? source.call(null, [a, i]) : source;
    if (index <= length + 1) {
      yield observableSource;
    } else {
      return observableSource;
    }
  }
}

export function mergeLatestFrom<T, O2 extends ObservableInput<any>>(
  source2: O2 | ((v1: T) => O2),
): OperatorFunction<T, [T, ObservedValueOf<O2>]>;
export function mergeLatestFrom<T, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>>(
  v2: O2 | ((v1: T) => O2),
  v3: O3 | ((v1: T) => O3),
  concurrent?: number,
): OperatorFunction<T, [T, ObservedValueOf<O2>, ObservedValueOf<O3>]>;
export function mergeLatestFrom<T, O2 extends ObservableInput<any>, O3 extends ObservableInput<any>, O4 extends ObservableInput<any>>(
  v2: O2 | ((v1: T) => O2),
  v3: O3 | ((v1: T) => O3),
  v4: O4 | ((v1: T) => O4),
  concurrent?: number,
): OperatorFunction<T, [T, ObservedValueOf<O2>, ObservedValueOf<O3>, ObservedValueOf<O4>]>;
export function mergeLatestFrom<
  T,
  O2 extends ObservableInput<any>,
  O3 extends ObservableInput<any>,
  O4 extends ObservableInput<any>,
  O5 extends ObservableInput<any>
>(
  v2: O2 | ((v1: T) => O2),
  v3: O3 | ((v1: T) => O3),
  v4: O4 | ((v1: T) => O4),
  v5: O5 | ((v1: T) => O5),
  concurrent?: number,
): OperatorFunction<T, [T, ObservedValueOf<O2>, ObservedValueOf<O3>, ObservedValueOf<O4>, ObservedValueOf<O5>]>;
export function mergeLatestFrom<
  T,
  O2 extends ObservableInput<any>,
  O3 extends ObservableInput<any>,
  O4 extends ObservableInput<any>,
  O5 extends ObservableInput<any>,
  O6 extends ObservableInput<any>
>(
  v2: O2 | ((v1: T) => O2),
  v3: O3 | ((v1: T) => O3),
  v4: O4 | ((v1: T) => O4),
  v5: O5 | ((v1: T) => O5),
  v6: O6 | ((v1: T) => O6),
  concurrent?: number,
): OperatorFunction<T, [T, ObservedValueOf<O2>, ObservedValueOf<O3>, ObservedValueOf<O4>, ObservedValueOf<O5>, ObservedValueOf<O6>]>;
export function mergeLatestFrom<T, R>(array: ObservableInput<any>[]): OperatorFunction<T, R>;

/* tslint:disable:max-line-length */
export function mergeLatestFrom<T, O extends ObservableInput<any>>(
  project: (value: T, index: number) => Observable<O>,
  concurrent?: number,
): OperatorFunction<T, ObservedValueOf<O>>;

export function mergeLatestFrom<T>(...inputs: any[]): OperatorFunction<T, any[]> {
  let concurrency: number;
  if (typeof inputs[inputs.length - 1] === 'number') {
    concurrency = inputs.pop();
  }

  const sources: ObservableSourceType[] = inputs;

  return (source: Observable<T>) =>
    source.pipe(mergeMap((a, i) => of(a).pipe(withLatestFrom<T, any[]>(...sourcesGen(sources, a, i))), concurrency));
}