r takes a unary function and creates a model of Output
        Iterator. Each item assigned to the output iterator is passed as an argument
        to the unary function. The motivation for this iterator is that creating
        a conforming output iterator is non-trivial, particularly because the proper
        implementation usually requires a proxy object.
      </p>
<h3>
<a name="iterator.specialized.function_output.h0"></a>
        <span class="phrase"><a name="iterator.specialized.function_output.exam