Joel Pobar's CLR weblog

hello, world... Reflection.Emit style!

Before I head home, I thought I'd post up your typical “Hello, World” style app in Reflection.Emit. ~20 lines of C# code, not too bad for code generation of a Console.WriteLine. For those who don't know what Reflection.Emit is, or what it can do, have a look here here and here for starters.

using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Threading;

public class EmitHelloWorld
{
      static void Main(string[] args)
      {
            // create a dynamic assembly and module 
            AssemblyName assemblyName = new AssemblyName(); 
            assemblyName.Name = "HelloWorld"; 
            AssemblyBuilder assemblyBuilder = Thread.GetDomain().DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.RunAndSave);
            ModuleBuilder module; 
            module = assemblyBuilder.DefineDynamicModule("HelloWorld.exe"); 
      
            // create a new type to hold our Main method
            TypeBuilder typeBuilder = module.DefineType("HelloWorldType", TypeAttributes.Public | TypeAttributes.Class);
            
            // create the Main(string[] args) method
            MethodBuilder methodbuilder = typeBuilder.DefineMethod("Main", MethodAttributes.HideBySig | MethodAttributes.Static | MethodAttributes.Public, typeof(void), new Type[] { typeof(string[]) });
            
            // generate the IL for the Main method
            ILGenerator ilGenerator = methodbuilder.GetILGenerator();
            ilGenerator.EmitWriteLine("hello, world");
            ilGenerator.Emit(OpCodes.Ret);
 
            // bake it
            Type helloWorldType = typeBuilder.CreateType();
 
            // run it
            helloWorldType.GetMethod("Main").Invoke(null, new string[] {null});
 
            // set the entry point for the application and save it
            assemblyBuilder.SetEntryPoint(methodbuilder, PEFileKinds.ConsoleApplication);
            assemblyBuilder.Save("HelloWorld.exe");
      }
}