--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/HowTo/Patterns/DuckTyping.cs	Thu Mar 27 21:46:09 2014 +0400
@@ -0,0 +1,78 @@
+using System;
+
+using NUnit.Framework;
+
+using BLToolkit.Patterns;
+
+namespace HowTo.Patterns
+{
+	//[TestFixture]
+	public class DuckTyping
+	{
+		// By default, all interface methods are optional.
+		// 
+		public interface OptionalInterface
+		{
+			// If the source object does not implement the [b]Method1[/b], a NotImplementedException is thrown at [i]run time[/i].
+			//
+			void Method1();
+
+			// If the source object does not implement the [b]Method2[/b], a TypeBuilderException is thrown at [i]build time[/i].
+			//
+			/*[a]*/[MustImplement]/*[/a]*/
+			void Method2();
+
+			// If the source object does not implement the [b]Method3[/b], an empty stub is genegated.
+			// The return value and all output parameters will be set to default values.
+			//
+			/*[a]*/[MustImplement(false, false)]/*[/a]*/
+			int Method3();
+		}
+
+		// The MustImplement attribute also can control the entire interface.
+		//
+		/*[a]*/[MustImplement]/*[/a]*/
+		public interface RequiredInterface
+		{
+			// If the source object does not implement the [b]Method1[/b], a TypeBuilderException is thrown at [i]build time[/i].
+			//
+			void Method1();
+
+			// If the source object does not implement the [b]Method2[/b], a NotImplementedException is thrown at [i]run time[/i].
+			//
+			/*[a]*/[MustImplement(false)]/*[/a]*/
+			void Method2();
+
+			// If the source object does not implement the [b]Method3[/b], an empty stub is genegated.
+			// The return value and all output parameters will be set to default values.
+			//
+			/*[a]*/[MustImplement(false, false)]/*[/a]*/
+			int Method3();
+		}
+
+		public class TestClass
+		{
+			public int Method3()
+			{
+				return 3;
+			}
+		}
+
+		// Two or more interfaces can be mixed together.
+		//
+		public interface InterfaceMix : RequiredInterface, OptionalInterface
+		{
+		}
+
+		//[Test]
+		public void Test()
+		{
+			InterfaceMix      duck = /*[a]*/BLToolkit.Patterns.DuckTyping.Implement/*[/a]*/<InterfaceMix>(new TestClass());
+			RequiredInterface duck1 = duck;
+			OptionalInterface duck2 = duck;
+
+			duck1.Method1();
+			duck2.Method1();
+		}
+	}
+}