Extension Methods for Deferred Log4Net Message Formatting

In a recent post I described some initial impressions of the MS Live Labs Simple Logging Framework (SLF).  One of the things I really like about SLF is the use of lambas as a way to defer execution of potentially slow or unchecked message formatting code.  I also railed on the idea of creating a completely new effort when log4net is an active open-source project.

So, here I am putting my money where my mouth is: I've created some extension methods for instances of ILog that accept lambdas - now if you use log4net in a C# 3.0+ environment, you can defer message formatting as easily as you can in SLF.  The code is quite simple:

using log4net;
namespace Log4NetExtensions
{    public static class Log4NetExtensionMethods    {        public static void Debug( this ILog log, Func<string> formattingCallback )        {            if( log.IsDebugEnabled )            {                log.Debug( formattingCallback() );            }        }        public static void Info( this ILog log, Func<string> formattingCallback )        {            if( log.IsInfoEnabled )            {                log.Info( formattingCallback() );            }        }        public static void Warn( this ILog log, Func<string> formattingCallback )        {            if( log.IsWarnEnabled )            {                log.Warn( formattingCallback() );            }        }        public static void Error( this ILog log, Func<string> formattingCallback )        {            if( log.IsErrorEnabled )            {                log.Error( formattingCallback() );            }        }        public static void Fatal( this ILog log, Func<string> formattingCallback )        {            if( log.IsFatalEnabled )            {                log.Fatal( formattingCallback() );            }        }     }
} 

Each method of the ILog interface gets its own override in the form of an extension method.  The method accepts a Func<string> that allows you to capture log message formatting in a lamba expression, and hence defer its execution until absolutely necessary (or avoid it altogether).  Here are some quick and dirty unit tests to demonstrate the basic use and functionality:

using NUnit.Framework;
namespace Log4NetExtensions.Tests
{    [TestFixture]    public class Log4NetExtensionTests    {        log4net.ILog Log;        log4net.Appender.MemoryAppender appender;        [TestFixtureSetUp]        public void FixtureSetUp()        {            Log = log4net.LogManager.GetLogger( System.Reflection.MethodBase.GetCurrentMethod().DeclaringType );            appender = new log4net.Appender.MemoryAppender             {                Name = "Memory Appender",                Threshold = log4net.Core.Level.Debug            };            log4net.Config.BasicConfigurator.Configure( appender );                                }        [SetUp]        public void TestSetUp()        {            appender.Clear();                        log4net.Core.LoggingEvent[] events = appender.GetEvents();            Assert.That( 0 == events.Length, "failed to clear appender of log events" );            Log.Logger.Repository.Threshold = log4net.Core.Level.Debug;        }        [Test]        public void LogViaLambdaTest()        {            Log.Debug( () => "Hello World!" );            log4net.Core.LoggingEvent[] events = appender.GetEvents();                                    Assert.That( 1 == events.Length, "failed to log via lamba" );            Assert.That(                 StringComparer.CurrentCulture.Equals(                     "Hello World!",                     events[ 0 ].RenderedMessage                                   ),                "rendered message does not match (via lambda)"            );        }        [Test]        public void LogWithLocalVariableReference()        {            string value = "World!";            Log.Debug( () => "Hello " + value );            log4net.Core.LoggingEvent[] events = appender.GetEvents();            Assert.That( 1 == events.Length, "failed to log with local variable reference" );            Assert.That(                StringComparer.CurrentCulture.Equals(                    "Hello World!",                    events[ 0 ].RenderedMessage                ),                "rendered message does not match (local variable reference)"            );        }        [Test]        public void LambdaIsNotEvaluatedAtInactiveLogLevel()        {                        Log.Logger.Repository.Threshold = log4net.Core.Level.Error;                     bool evaluated = false;            Log.Debug( () =>                 {                     evaluated = true;                    return "Hello World!";                }            );            Assert.That( ! evaluated, "lamba was evaluated at inactive log level" );            Log.Error( () =>                {                    evaluated = true;                    return "Hello World!";                }            );            Assert.That( evaluated, "lamba was not evaluated at active log level" );        }    }
}

Play with it, see if you like it.  I will to.  Any suggestions or comments are encouraged.  If there is enough interest I'll see about submitting the extensions to the apache project.