e class="programlisting"><span class="keyword">struct</span> <span class="identifier">storage_policy</span>
<span class="special">{</span>
    <span class="comment">// Value is the same type as typename MultiPass::value_type</span>
    <span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">Value</span><span class="special">&gt;</span>
    <span class="keyword">struct</span> <span class="identifier">unique</span>
    <span class="