ll result in this library calling <code class="computeroutput"><code class="computeroutput"><a class="link" href="old_failure.html" title="Function old_failure">boost::contract::old_failure</a></code></code> (because old values could not be copied to check postconditions and exception guarantees). This functor should capture old value pointers by references so they can be assigned (all other variables needed to evaluate old value expressions can be captured by (constant) value, or better by (constant) refer