using System;
using System.Reflection;

class Program {
    class Duck { public string Speak() { return "quack"; } }

    // *** before: ***
    // a member of a type unknown at compile time was reached through
    // reflection: find it by name, then Invoke it and cast the result
    static string SpeakOld(object thing) {
        MethodInfo method = thing.GetType().GetMethod("Speak");
        return (string)method.Invoke(thing, null);
    }

    // *** in version 4.0: ***
    // dynamic postpones the whole call to run time
    static string SpeakNew(dynamic thing) {
        return thing.Speak();
    }

    static void Main() {
        Duck duck = new Duck();
        Console.WriteLine(SpeakOld(duck));
        Console.WriteLine(SpeakNew(duck));

        dynamic value = 2;
        Console.WriteLine(value + 3);        // 5, addition of numbers
        value = "two";
        Console.WriteLine(value + "3");      // two3, joining of strings

        // the price: a mistake is no longer a compiler error
        try {
            Console.WriteLine(SpeakNew(42));
        } catch (Exception e) {
            Console.WriteLine(e.GetType().Name);   // RuntimeBinderException
        }
    }
}