Introducing DynamicWrapper

Shout it kick it on

DynamicWrapper project on CodePlex

Edit: DynamicWrapper does not work in SIlverlight as I first though.  My unit tests passed, but in runtime I get an exception when I try to use the class.  I will be looking at some alternatives.

Over the past few weeks, I have been working on a utility that I have wanted for years: something that allows me to apply an interface to an object that matches the contract but doesn’t actually implement the interface.  In other words, I’ve wanted duck typing in C#.  The code and project can be found on CodePlex.  It is set up so you simply copy one file into your solution and use the extension methods.

Why did I want this?  Because I write a lot of unit tests and I develop in .Net with C#.  Because I write way too many wrapper classes to make my code testable.  For example, lets say that I have a class that I want to test and it acts upon a framework object:

public sealed class FrameworkClass
    internal FrameworkClass() {}

    public int X {get; set;}
    public int Y {get; set;}
    public int Calculate() { return DoSomeStuff(); }

public class MyClass
    public void DoSomethingWithFrameworkData(FrameworkClass value)
        // Do Something

The problem is that I can’t test MyClass because it is dependent upon FrameworkClass which I can never construct myself (it is sealed with an internal constructor and no interface).  The solution for this is simple but tedious – create a wrapper class that implements an interface and proxy through the wrapper class to the real object.  This approach works, but I can say this: I am sick of writing wrapper classes!

This is why I created this DynamicWrapper utility.  It exposes two extension methods: realObject.As<Interface>() and wrapper.AsReal<ConcreteClass>().  It uses Reflection to emit a dynamically generated wrapper class that implements the interface, and wraps your object for you.  It sounds complicated, but it is extremely simple to use.

Here is an example. Start by creating an interface that looks like the FrameworkClass:

public interface ICalculatable
    int X {get; set;}
    int Y {get; set;}
    int Calculate();

Modify your class to depend on ICalculatable:

public void DoSomethingWIthFrameworkData(ICalculatable value) {}

Now, when you pass the framework class into the MyClass, you can wrap it with the interface:


If you need the framework object to pass back to the framework, it is really simple:


That’s all there is to it!  The utility is very simple.  It just gets me out of the business of writing (and maintaining) wrapper classes. I am now free to get back to real development.

*On a slightly related note, I will be focusing my learning efforts towards Ruby in the coming months.*

Leave a Reply