# Maps every element to a nested structure then flattens it
        #
        # ~~~~nitish
        # fun chars_fn(s: String): Iterator[Char]
        # do
        #       return s.chars.iterator
        # end
        # var cs = ["aaa","bbb","ccc"]
        # assert cs.iterator.flat_map(&chars_fn).to_a.join == "aaabbbccc"
        # ~~~~
        fun flat_map(f: Fun1[E, Iterator[Object]]): FlatMapIter[E, Object]
        do
                return new FlatMapIter[E, Object](self, f)
        end