"hash.changes.boost_1_64_0"></a></span><a class="link" href="changes.html#hash.changes.boost_1_64_0">Boost
      1.64.0</a>
    </h3>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
          Fix for recent versions of Visual C++ which have removed <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unary_function</span></code> and <code class="computeroutput"><span class="identifier"