sebnilsson.com | Liquid Development Is What I Do
Seb Nilsson

Convert C# Anonymous (or Any) Types Into Dynamic ExpandoObject

There are scenarios when you need to convert an anonymous type in C#, or any other type, into a dynamic, or more specifically to the underlying ExpandoObject-type.

My specific need was to be able to move the data from an anonymous type from the current assembly into a dynamically executed external assembly. So I created an extension-method for this, which moves all the properties from any object into a new ExpandoObject.

public static ExpandoObject ToExpandoObject(this object obj)
{
    // Null-check

    IDictionary expando = new ExpandoObject();

    foreach (PropertyDescriptor property in TypeDescriptor.GetProperties(obj.GetType()))
    {
        expando.Add(property.Name, property.GetValue(obj));
    }

    return (ExpandoObject) expando;
}

You can use the extension-method on any type of object and choose to reference the resulting type by it's actual type ExpandoObject or as a dynamic.

var anonymous = new {Id = 123, Text = "Abc123", Test = true};

dynamic dynamicObject = anonymous.ToExpandoObject();
ExpandoObject expandoObject = anonymous.ToExpandoObject();

Since the code uses the type System.ComponentModel.TypeDescriptor, if you use .NET Core or .NET Standard, you might need to reference the Nuget-package named System.ComponentModel.TypeConverter.

C# 4: Reflected Dynamics

In Scott Hanselman's blog-entry titled Back to Basics: C# 4 method overloading and dynamic types , Scott talks about method-overloads in C# 4 and the dynamic -keyword.

class Program {
    static void f(Int32 x) { }
    static void f(dynamic x) {}
    static void f(Int32 x, dynamic y) {}
    static void f(dynamic x, Int32 y) {}
    static void f(Int32 x, dynamic y, Int32 z) {}
    static void f(dynamic x, Int32 y, dynamic z) {}
    static void Main(string[] args) {
        f(10); // Works - obvious
        f(10, 10); // Ambiguous - obvious
        f(10, 10, 10); // Ambiguous - not so obvious - since it should be possible to resolve
    }
}

...the behavior is totally by design:

  • dynamic in method signatures doesn’t come into it: it behaves like System.Object does.
  • Given that, neither of the ternary signatures is better because each fits better than the other on some arguments (Int32 fits 10 better than object does)

The key point here, in bold, because it's significant is: having the type dynamic means "use my runtime type for binding".

It all becomes very clear when Reflector is used on the code. This loosens up some thought-patterns and makes it easier to really understand the dynamic -keyword.

Another way to look at this is with Reflector. This C# code:

static void f(Int32 x, dynamic y, Int32 z) {}

is essentially this, from a method signature point of view:

static void f(int x, [Dynamic] object y, int z) {}

and if there was a method that returned dynamic, it'd look like this:

[return: Dynamic]
        private static object GetCalculator() {}