using Dynamic to add methods?

Question

Im trying to add function on runtime , something like that :

static void Main()
{
 dynamic d = new Duck();
 d.Quack =(Action) (() => Console.WriteLine("1")); //decalre a new method on runtime ??
 d.Quack(); 

}

public class Duck : System.Dynamic.DynamicObject
{
   //...
}

'UserQuery.Duck' does not contain a definition for 'Quack'

Isnt dynamic should allow me to do it ?

does brand new ExpandoObject is the only solution ?

i have my Duck class already. how can i make it Expando ? - can i make duck act like expando ?

Megathere

For some absolutely obscure reasons my post was deleted. By the way, you can not derive from ExpandoObject, and if you want to have your object behaves like that one, you have 2 solutions, imo: 1. Create Expando and add initially all properties and methods you have in Duck, and do not use Duck. 2. Generate your own ExpandoObject. Look here: Dynamic Behaviour on Objects at Runtime With Custom ExpandoObject for more detailed example and derive Duck from it. – Burdette

Answer 1

You can't add properties of any type (even functions) to an existing type.

dynamic d = new Duck();
d.Quack = "Quack";//fails because there is no such property on duck

You could use ExpandoObject though:

dynamic d = new ExpandoObject();
d.Quack = (Action)(() => System.Console.WriteLine("1"));
d.Quack(); 

---

Don't be confused with what the dynamic type does.

void speak(dynamic d)
{
 d.Quack();//this is NOT checked at compile time
}

Now I can do : speak(new Duck()); and speak(new Goose()); , it will compile and run if both Duck and Goose have the method Quack(), if they don't, it raises an exception. (The same one you get)

When you call a method/property on a dynamic type, it only resolves that at runtime and doesn't do a compiler check.

The ExpandoObject allows you to create properties on the fly.

---

To answer your question on the comment, the way I see it is, if you need your own class which needed the ability to create new properties you could inherit from DynamicObject. Like this (adapted from this msdn page):

class DynamicDuck : DynamicObject 
{
      Dictionary<string, object> dictionary
           = new Dictionary<string, object>();
    public int Count
    {
        get
        {
           return dictionary.Count;
        }
     }
    public override bool TryGetMember(
          GetMemberBinder binder, out object result)
    {
          string name = binder.Name.ToLower();
            return dictionary.TryGetValue(name, out result);
    }
    public override bool TrySetMember(
         SetMemberBinder binder, object value)
    {
          dictionary[binder.Name.ToLower()] = value;
          return true;
    }
 }

Then you could do:

dynamic d = new DynamicDuck();
d.firstname = "Gideon";
d.Quack = (Action)(() => System.Console.WriteLine("Quack"));

Eclectic

thnaks but why would i ever want to inherit from System.Dynamic.DynamicObject? the only scenario I see - is to override the tryGetXXX etc.. methods.... – Megathere

If you don't want to use your class as a "dictionary", e.g. if it is represents an xml or csv file where you can access columns and elements dynamically, like file.nameOfSecondColumn[row] – Selfdevotion