style="white-space:nowrap">f:<span class="type">L</span>&nbsp;&#8209;&gt;&nbsp;<span class="type">Void</span></span>):<span class="type">Void</span></code></p></h3><div class="doc"><p></p></div></div><div class="field "><a name="ensure"></a><h3><p><code><span class="label">static</span><a href="#ensure"><span class="identifier">ensure</span></a>&lt;<span class="type">L</span>, <span class="type">R</span>&gt; (<span style="white-space:nowrap">either:<a class="type" title="Either wraps one value of two possib