Creating code contract invariant
Something that is defined as invariant tells us that it will never change. It will always be the same, no matter what. This brings up a vast array of use cases if we consider this in the context of code contracts. The invariant code contract is basically used to validate the internal state of a class. So, what do we mean by the "internal state?" Well, the properties of the class give that class a specific state. Let's assume that we wanted to guarantee that the properties of the class we are using only accept specific values, thereby assuring the internal state of that class. This is where the code contract invariant comes into play.
Getting ready
You can understand the use of the invariant better with the use of the following example. Assume that the class needs to store dates. We can't ever store a date in the past though. Any date used in the class must be a current or future date.
How to do it…
Before you go on, ensure that you have added the code contracts...
