C# Advanced Concepts

The dynamic type enables the operations in which it occurs to bypass compile-time type checking. Instead, these operations are resolved at run time.

Thedynamic type simplifies access to COM APIs such as the Office Automation APIs

 dynamic dyn = 1;
        object obj = 1;

        // Rest the mouse pointer over dyn and obj to see their 
        // types at compile time.
        System.Console.WriteLine(dyn.GetType());
        System.Console.WriteLine(obj.GetType());

A compiler error is reported for the attempted addition of an integer and an object in expression obj + 3. However, no error is reported for dyn + 3. The expression that contains dyn is not checked at compile time because the type of dyn is dynamic.

XElement contactXML =
    new XElement("Contact",
        new XElement("Name", "Patrick Hines"),
        new XElement("Phone", "206-555-0144"),
        new XElement("Address",
            new XElement("Street1", "123 Main St"),
            new XElement("City", "Mercer Island"),
            new XElement("State", "WA"),
            new XElement("Postal", "68042")
        )
    );

dynamic contact = new ExpandoObject();
contact.Name = "Patrick Hines";
contact.Phone = "206-555-0144";
contact.Address = new ExpandoObject();
contact.Address.Street = "123 Main St";
contact.Address.City = "Mercer Island";
contact.Address.State = "WA";
contact.Address.Postal = "68402";

Use of  dynamic objects is the ability to create extensible objects - objects that start out with a set of static members and then can add additional properties and even methods dynamically.

dynamic expand = new ExpandoObject();

expand.Name = "Rick";
expand.HelloWorld = (Func<string, string>) ((string name) => 
{ 
    return "Hello " + name; 
});

Console.WriteLine(expand.Name);
Console.WriteLine(expand.HelloWorld("Dufus"));
So, if you need to handle a dynamic type: use dynamic and if you need to handle dynamic data such as XML or JSON: use ExpandoObject