Question

Not so long ago I started to learn to use System.Reflection.Emit namespace. I’m now trying to translate this code to use of ILGenerator:

MyClass c = new MyClass("MyClass");
c.Do(":D");

For this piece of code I have three questions: how to create object? how to call contructor and how to call method of class? Please help.

Answer 1

Here’s a complete example that shows the necessary IL code.

You can test this in LINQPad:

void Main()
{
    // Manual test first
    MyClass c = new MyClass("MyClass");
    c.Do(":D");

    var method = new DynamicMethod("dummy", null, Type.EmptyTypes);
    var il = method.GetILGenerator();

    // <stack> = new MyClass("MyClass");
    il.Emit(OpCodes.Ldstr, "MyClass");
    il.Emit(OpCodes.Newobj, typeof(MyClass).GetConstructor(new[] { typeof(string) }));

    // <stack>.Do(":D");
    il.Emit(OpCodes.Ldstr, ":D");
    il.Emit(OpCodes.Call, typeof(MyClass).GetMethod("Do", new[] { typeof(string) }));

    // return;
    il.Emit(OpCodes.Ret);

    var action = (Action)method.CreateDelegate(typeof(Action));
    action();
}

public class MyClass
{
    public MyClass(string text)
    {
        Console.WriteLine("MyClass(" + text + ")");
    }

    public void Do(string text)
    {
        Console.WriteLine("Do(" + text + ")");
    }
}

Output:

MyClass(MyClass)
Do(:D)
MyClass(MyClass)
Do(:D)

---

Incidentally, you can use LINQPad to get hold of the IL code for a particular example. Let me cut out the IL-part of the above example, like this (I removed the class as well, it’s the same class):

void Main()
{
    MyClass c = new MyClass("MyClass");
    c.Do(":D");
}

By executing this code, and then using the IL tab of the output, you can see the generated code:

The two instructions stloc.0 and ldloc.0 is the variable in the code.

The IL I emitted first is akin to this piece of code:

new MyClass("MyClass").Do(":D");

ie. no variable, just temporary storage on the stack, and indeed: