source.cs

// <Snippet1>
using System;
using System.Threading;
using System.Reflection;
using System.Reflection.Emit;

class TestILGenerator
{
  	public static Type DynamicDotProductGen()
	{
	   Type ivType = null;
	   Type[] ctorParams = new Type[] { typeof(int),
		               		    typeof(int),
					    typeof(int)};
 	
	   AppDomain myDomain = Thread.GetDomain();
	   AssemblyName myAsmName = new AssemblyName();
	   myAsmName.Name = "IntVectorAsm";
	
	   AssemblyBuilder myAsmBuilder = myDomain.DefineDynamicAssembly(
					  myAsmName,
					  AssemblyBuilderAccess.RunAndSave);

   	   ModuleBuilder IntVectorModule = myAsmBuilder.DefineDynamicModule("IntVectorModule",
									    "Vector.dll");

	   TypeBuilder ivTypeBld = IntVectorModule.DefineType("IntVector",
						              TypeAttributes.Public);

	   FieldBuilder xField = ivTypeBld.DefineField("x", typeof(int),
                                                       FieldAttributes.Private);
	   FieldBuilder yField = ivTypeBld.DefineField("y", typeof(int),
                                                       FieldAttributes.Private);
	   FieldBuilder zField = ivTypeBld.DefineField("z", typeof(int),
                                                       FieldAttributes.Private);

           Type objType = Type.GetType("System.Object");
           ConstructorInfo objCtor = objType.GetConstructor(new Type[0]);

	   ConstructorBuilder ivCtor = ivTypeBld.DefineConstructor(
					  MethodAttributes.Public,
					  CallingConventions.Standard,
					  ctorParams);
	   ILGenerator ctorIL = ivCtor.GetILGenerator();
           ctorIL.Emit(OpCodes.Ldarg_0);
           ctorIL.Emit(OpCodes.Call, objCtor);
           ctorIL.Emit(OpCodes.Ldarg_0);
           ctorIL.Emit(OpCodes.Ldarg_1);
           ctorIL.Emit(OpCodes.Stfld, xField);
           ctorIL.Emit(OpCodes.Ldarg_0);
           ctorIL.Emit(OpCodes.Ldarg_2);
           ctorIL.Emit(OpCodes.Stfld, yField);
           ctorIL.Emit(OpCodes.Ldarg_0);
           ctorIL.Emit(OpCodes.Ldarg_3);
           ctorIL.Emit(OpCodes.Stfld, zField);
	   ctorIL.Emit(OpCodes.Ret);

	   // This method will find the dot product of the stored vector
	   // with another.

	   Type[] dpParams = new Type[] { ivTypeBld };

           // Here, you create a MethodBuilder containing the
	   // name, the attributes (public, static, private, and so on),
	   // the return type (int, in this case), and a array of Type
	   // indicating the type of each parameter. Since the sole parameter
	   // is a IntVector, the very class you're creating, you will
	   // pass in the TypeBuilder (which is derived from Type) instead of
	   // a Type object for IntVector, avoiding an exception.

	   // -- This method would be declared in C# as:
	   //    public int DotProduct(IntVector aVector)

           MethodBuilder dotProductMthd = ivTypeBld.DefineMethod(
	    		                  "DotProduct",
				          MethodAttributes.Public,
                                          typeof(int),
                                          dpParams);

	   // A ILGenerator can now be spawned, attached to the MethodBuilder.

	   ILGenerator mthdIL = dotProductMthd.GetILGenerator();
	
 	   // Here's the body of our function, in MSIL form. We're going to find the
	   // "dot product" of the current vector instance with the passed vector
	   // instance. For reference purposes, the equation is:
	   // (x1 * x2) + (y1 * y2) + (z1 * z2) = the dot product

	   // First, you'll load the reference to the current instance "this"
	   // stored in argument 0 (ldarg.0) onto the stack. Ldfld, the subsequent
	   // instruction, will pop the reference off the stack and look up the
	   // field "x", specified by the FieldInfo token "xField".

	   mthdIL.Emit(OpCodes.Ldarg_0);
	   mthdIL.Emit(OpCodes.Ldfld, xField);

	   // That completed, the value stored at field "x" is now atop the stack.
	   // Now, you'll do the same for the object reference we passed as a
	   // parameter, stored in argument 1 (ldarg.1). After Ldfld executed,
	   // you'll have the value stored in field "x" for the passed instance
	   // atop the stack.

	   mthdIL.Emit(OpCodes.Ldarg_1);
	   mthdIL.Emit(OpCodes.Ldfld, xField);

           // There will now be two values atop the stack - the "x" value for the
	   // current vector instance, and the "x" value for the passed instance.
	   // You'll now multiply them, and push the result onto the evaluation stack.

	   mthdIL.Emit(OpCodes.Mul_Ovf_Un);

	   // Now, repeat this for the "y" fields of both vectors.

	   mthdIL.Emit(OpCodes.Ldarg_0);
	   mthdIL.Emit(OpCodes.Ldfld, yField);
	   mthdIL.Emit(OpCodes.Ldarg_1);
	   mthdIL.Emit(OpCodes.Ldfld, yField);
	   mthdIL.Emit(OpCodes.Mul_Ovf_Un);

	   // At this time, the results of both multiplications should be atop
	   // the stack. You'll now add them and push the result onto the stack.

	   mthdIL.Emit(OpCodes.Add_Ovf_Un);

	   // Multiply both "z" field and push the result onto the stack.
	   mthdIL.Emit(OpCodes.Ldarg_0);
	   mthdIL.Emit(OpCodes.Ldfld, zField);
	   mthdIL.Emit(OpCodes.Ldarg_1);
	   mthdIL.Emit(OpCodes.Ldfld, zField);
	   mthdIL.Emit(OpCodes.Mul_Ovf_Un);

	   // Finally, add the result of multiplying the "z" fields with the
	   // result of the earlier addition, and push the result - the dot product -
	   // onto the stack.
	   mthdIL.Emit(OpCodes.Add_Ovf_Un);

	   // The "ret" opcode will pop the last value from the stack and return it
	   // to the calling method. You're all done!

	   mthdIL.Emit(OpCodes.Ret);

 	   ivType = ivTypeBld.CreateType();

	   return ivType;
 	}

	public static void Main() {
	
	   Type IVType = null;
           object aVector1 = null;
           object aVector2 = null;
	   Type[] aVtypes = new Type[] {typeof(int), typeof(int), typeof(int)};
           object[] aVargs1 = new object[] {10, 10, 10};
           object[] aVargs2 = new object[] {20, 20, 20};
	
	   // Call the  method to build our dynamic class.

	   IVType = DynamicDotProductGen();

           Console.WriteLine("---");

	   ConstructorInfo myDTctor = IVType.GetConstructor(aVtypes);
	   aVector1 = myDTctor.Invoke(aVargs1);
	   aVector2 = myDTctor.Invoke(aVargs2);

	   object[] passMe = new object[1];
           passMe[0] = (object)aVector2;

	   Console.WriteLine("(10, 10, 10) . (20, 20, 20) = {0}",
			     IVType.InvokeMember("DotProduct",
						  BindingFlags.InvokeMethod,
						  null,
						  aVector1,
						  passMe));

	   // +++ OUTPUT +++
	   // ---
	   // (10, 10, 10) . (20, 20, 20) = 600
	}
}
// </Snippet1>