Is it possible to specify code contracts to ensure that method doesn't change state of object

Question

Lets say I got a boolean IsValid property on my object.

I would like to create a method, and ensure that IsValid isn't changed after calling it, whether it was true or false before the call.

Is there a support for such thing?

Answer 1

I haven't tried it myself, but according to the MSDN Contract.OldValue might help to check that a single property value has not changed:

public bool IsValid
{
  get
  {
    ...
  }
}

public void SomeMethod()
{
  Contract.Ensures(this.IsValid == Contract.OldValue(this.IsValid));
  ...
}