Bambit Technologies: Custom Software Development

The following is an example of extending the ILog interface in the log4net libraries. See this blog entry for an explination.
    
    public static class LogExtension
    {
        /// &lt;summary&gt;
        /// Logs an exception and then returns that exception
        /// &lt;/summary&gt;
        /// &lt;span  name="logger" class="mceItemParam"&gt;&lt;/span&gt;The logger this method overrides.&lt;/param&gt;
        /// &lt;span  name="message" class="mceItemParam"&gt;&lt;/span&gt;The message to log.&lt;/param&gt;
        /// &lt;span  name="exception" class="mceItemParam"&gt;&lt;/span&gt;The exception to log.&lt;/param&gt;
        /// &lt;returns&gt;The &lt;see cref="exception"/&gt; passed in, unmodified&lt;/returns&gt;
        public static Exception Exception(this ILog logger, Exception exception, string message  )
        {
            logger.Error(message, exception);
            return exception;
        }
        /// &lt;summary&gt;
        /// Logs an exception and then returns that exception
        /// &lt;/summary&gt;
        /// &lt;span  name="logger" class="mceItemParam"&gt;&lt;/span&gt;The logger this method overrides.&lt;/param&gt;
        /// &lt;span  name="exception" class="mceItemParam"&gt;&lt;/span&gt;The exception to log.&lt;/param&gt;
        /// &lt;span  name="fmt" class="mceItemParam"&gt;&lt;/span&gt;The format string for the message to log.&lt;/param&gt;
        /// &lt;span  name="arg0" class="mceItemParam"&gt;&lt;/span&gt;The argument for the format string.&lt;/param&gt;
        /// &lt;returns&gt;
        /// The &lt;see cref="exception"/&gt; passed in, unmodified
        /// &lt;/returns&gt;
        public static Exception Exception(this ILog logger, Exception exception, string fmt, object arg0)
        {
            logger.Error(string.Format(fmt, arg0), exception);
            return exception;
        }
        /// &lt;summary&gt;
        /// Logs an exception and then returns that exception
        /// &lt;/summary&gt;
        /// &lt;span  name="logger" class="mceItemParam"&gt;&lt;/span&gt;The logger this method overrides.&lt;/param&gt;
        /// &lt;span  name="exception" class="mceItemParam"&gt;&lt;/span&gt;The exception to log.&lt;/param&gt;
        /// &lt;span  name="fmt" class="mceItemParam"&gt;&lt;/span&gt;The format string for the message to log.&lt;/param&gt;
        /// &lt;span  name="arg0" class="mceItemParam"&gt;&lt;/span&gt;The first argument for the format string.&lt;/param&gt;
        /// &lt;span  name="arg1" class="mceItemParam"&gt;&lt;/span&gt;The second argument for the format string.&lt;/param&gt;
        /// &lt;returns&gt;
        /// The &lt;see cref="exception"/&gt; passed in, unmodified
        /// &lt;/returns&gt;
        public static Exception Exception(this ILog logger, Exception exception, string fmt, object arg0, object arg1)
        {
            logger.Error(string.Format(fmt, arg0,arg1), exception);
            return exception;
        }

        /// &lt;summary&gt;
        /// Logs an exception and then returns that exception
        /// &lt;/summary&gt;
        /// &lt;span  name="logger" class="mceItemParam"&gt;&lt;/span&gt;The logger this method overrides.&lt;/param&gt;
        /// &lt;span  name="exception" class="mceItemParam"&gt;&lt;/span&gt;The exception to log.&lt;/param&gt;
        /// &lt;span  name="fmt" class="mceItemParam"&gt;&lt;/span&gt;The format string for the message to log.&lt;/param&gt;
        /// &lt;span  name="arg0" class="mceItemParam"&gt;&lt;/span&gt;The first argument for the format string.&lt;/param&gt;
        /// &lt;span  name="arg1" class="mceItemParam"&gt;&lt;/span&gt;The second argument for the format string.&lt;/param&gt;
        /// &lt;span  name="arg2" class="mceItemParam"&gt;&lt;/span&gt;The third argument for the format string.&lt;/param&gt;
        /// &lt;returns&gt;
        /// The &lt;see cref="exception"/&gt; passed in, unmodified
        /// &lt;/returns&gt;
        public static Exception Exception(this ILog logger, Exception exception, string fmt, object arg0, object arg1, object arg2)
        {
            logger.Error(string.Format(fmt, arg0,arg1, arg2), exception);
            return exception;
        }
        /// &lt;summary&gt;
        /// Logs an exception and then returns that exception
        /// &lt;/summary&gt;
        /// &lt;span  name="logger" class="mceItemParam"&gt;&lt;/span&gt;The logger this method overrides.&lt;/param&gt;
        /// &lt;span  name="exception" class="mceItemParam"&gt;&lt;/span&gt;The exception to log.&lt;/param&gt;
        /// &lt;span  name="fmt" class="mceItemParam"&gt;&lt;/span&gt;The format string for the message to log.&lt;/param&gt;
        /// &lt;span  name="args" class="mceItemParam"&gt;&lt;/span&gt;The arguments for the format string.&lt;/param&gt;
        /// &lt;returns&gt;
        /// The &lt;see cref="exception"/&gt; passed in, unmodified
        /// &lt;/returns&gt;
        public static Exception Exception(this ILog logger, Exception exception, string fmt, params object[] args)
        {
            logger.Error(string.Format(fmt, args), exception);
            return exception;
        }
    }
log4net-Extension-Code.aspx