Removing delegates from chain

Question

class Program
{
    internal delegate int CallBack(int i);

    static void Main(string[] args)
    {
        CallBack callbackMethodsChain = null;
        CallBack cbM1 = new CallBack(FirstMethod);
        CallBack cbM2 = new CallBack(SecondMethod);

        callbackMethodsChain += cbM1;
        callbackMethodsChain += cbM2;

        Delegate.Remove(callbackMethodsChain, cbM1);
    /*L_0039: call class [mscorlib]System.Delegate [mscorlib]System.Delegate::Remove(class  [mscorlib]System.Delegate, class [mscorlib]System.Delegate)
        L_003e: pop 
        L_003f: ldloc.0 */

        Trace.WriteLine(callbackMethodsChain.GetInvocationList().Length);
        //Output: 2 **WTF!!!**


        callbackMethodsChain -= cbM1;
        /*
    L_0054: call class [mscorlib]System.Delegate [mscorlib]System.Delegate::Remove(class   [mscorlib]System.Delegate, class [mscorlib]System.Delegate)
          L_0059: castclass Generics.Program/CallBack
          L_005e: stloc.0 
          L_005f: ldloc.0 
        */
        Trace.WriteLine(callbackMethodsChain.GetInvocationList().Length);
        //Output: 1
    }

    private static int FirstMethod(int test)
    {            
        Trace.WriteLine("FirstMethod");
        return test;
    }

    private static int SecondMethod(int test)
    {
        Trace.WriteLine("SecondMethod");
        return test;
    }
}

So, we always need to cast (CallBack)Delegate.Remove(callbackMethodsChain, cbM1); to remove delegate from chain. It's not obviously.

Answer 1

A delegate is immutable, which means you cannot change it. Any methods that seems to change it, like "adding" to it or "subtracting" from it, actually returns a new delegate with the changes.

So this would not work:

a.Remove(b);

But this would:

a = a.Remove(b);

in terms of calling the Remove method that is.

Note that the following syntax does the right thing:

a -= b;

This is why, after calling Remove, that you still observe the code calling the delegate you seemingly removed, you're still calling the original delegate chain with that delegate present.

Answer 2

Some Other points are

Duplicates are allowed in your delegate i.e your delegate can have something like [cbM1,cbM2,cbM2,cbM3]

If u have method group [cbM1,cbM2, cbM3,cbM4,cbM5,cbM1,cbM2] and you perform some operation like [cbM1,cbM2, cbM3,cbM4,cbM5,cbM1,cbM2] - [cbM1,cbM2] then you will get [cbM1,cbM2, cbM3,cbM4,cbM5]

If u have [cbM1,cbM2, cbM3,cbM4,cbM5] and you perform some operation like [cbM1,cbM2, cbM3,cbM4,cbM5]-[cbM1,cbM5] you will get [cbM1,cbM2, cbM3,cbM4,cbM5]