Small sample of using Code Contracts

I had read about Code Contracts long time ago, but I didn’t see a reason to use contract instead of simple tests and argument's check with Exception's throws. Only now I’m trying to use them at real project. I didn’t see why I need to write:

Contract.Requires<ArgumentNullException>(argument == null); 

Instead of like I did it before:

if (argument == null) 

    throw new ArgumentNullException(“argument”)

Couple of weeks ago I had reinstall my Windows 7 on my laptop (I bought SSD for my laptop). After I install ReSharper with Visual Studio 2010 after run I accidental choosed “Go to the metadata” instead of like usual “Go to Object Explorer” by Ctrl and Mouse Click. So when I clicked on some class of System.xxx (basic classes of .NET) I looked at source code of these classes and found that they are using Code Contracts. I thought this is why I need to understand why I need to use contracts in my code, so I started to use them in some small applications and tried to find some interesting case. Read more...