title: Show line number object is destructed
body: <p>I'm implementing a trace mechanism that outputs a log line when a function is entered and upon exit (when the trace object is destructed).  I would be interested in also outputting the line number the scope exits but not sure how to accomplish this since the object is destroyed upon exit.  Obviously <code>__LINE__</code> in the destructor won't work since it will just output the destructor's line number.</p>