@Override public <A>CompletableFuture<A[]> toArray(final IntFunction<A[]> generator){
  return CompletableFuture.supplyAsync(null,exec);
}

@ Override public < A > CompletableFuture < A [ ] > toArray ( final IntFunction < A [ ] > generator ) { return CompletableFuture . supplyAsync ( null , exec ) ; }
asyncrhonously generate an array
