code: public <R> Stream<R> cast(final Class<R> c) {
          return map(new Func1<T, R>() {
              @Override
              public R call(T obj) {return c.cast(obj);}
          });
      }
docs: Returns a stream that contains all values of the original stream that has been casted to a given class type.
  
  @param c   a class to cast into
  @param <R> a type of the class
  @return a stream that contains all values of the original stream that has been casted to a given class type.