 throws.</p>
<p><span class="bold"><strong>Note</strong></span>: This function can be more efficient than calling upper_bound and lower_bound for lower_key and upper_key.</p>
<p><span class="bold"><strong>Note</strong></span>: Experimental function, the interface might change. </p>
</li>
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<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> KeyType<span class="special">,</span> <span class="keyword">typena