code: public static <T> MutableLongCollection collectLong(
              Iterable<T> iterable,
              LongFunction<? super T> longFunction)
      {
          if (iterable instanceof MutableCollection)
          {
              return ((MutableCollection<T>) iterable).collectLong(longFunction);
          }
          if (iterable instanceof ArrayList)
          {
              return ArrayListIterate.collectLong((ArrayList<T>) iterable, longFunction);
          }
          if (iterable instanceof List)
          {
              return ListIterate.collectLong((List<T>) iterable, longFunction);
          }
          if (iterable != null)
          {
              return IterableIterate.collectLong(iterable, longFunction);
          }
          throw new IllegalArgumentException("Cannot perform a collectLong on null");
      }
docs: Returns a new {@code long} collection with the results of applying the specified longFunction for each element of the iterable.
  <p>
  Example using a Java 8 lambda expression:
  <pre>
  MutableLongCollection longs =
  Iterate.<b>collectLong</b>(people, person -> person.getGuid());
  </pre>
  <p>
  Example using an anonymous inner class:
  <pre>
  MutableLongCollection longs =
  Iterate.<b>collectLong</b>(people,
  new LongFunction&lt;Person&gt;()
  {
  public long longValueOf(Person person)
  {
  return person.getGuid();
  }
  });
  </pre>