One cute feature of C# 1.0 was the introduction of the Conditional attribute. When you apply the conditional attribute to a method, calls to this method are only included in the resulting code if the appropriate define is set.

For instance, consider:

	[Conditional ("DEBUG")]
	void Log (string format, params object [] args)
	{
		Console.WriteLine (String.Format (format, args));
	}
	

Calls to Foo.Log become no-ops unless you pass the -define:DEBUG command line option to the compiler.

What is interesting about this compiler-supported feature is that that the code inside the method Log is checked for errors during compilation as any other regular method. They are first class citizens.