 public member functions</h3>
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<pre class="literallayout"><span class="identifier">index_type</span> <a name="idm14159-bb"></a><span class="identifier">index</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">value_type</span> <span class="special">&amp;</span> x<span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special"