sions"</a> by Kevlin Henney, <span class="emphasis"><em>C++
    Report</em></span> 12(7), July/August 2000) is a variant value type
    based on the second category. It supports copying of any value
    type and safe checked extraction of that value strictly against
    its type. A similar design, offering more appropriate operators,
    can be used for a generalized function adaptor,
    <code class="computeroutput">any_function</code>, a generalized iterator adaptor,
    <code class="computeroutput">any_i