Question

Is there a way to specify code contract requirements that are cross-cutting, for example a contract at the class level to require an instance variable to be non-null whenever any instance method on that class is invoked, or else the call will fail?

I’m new to code contracts and have been skimming the Feb 4, 2011 Code Contracts User Manual (PDF) and the MSDN docs but nothing pops out at me about cross-cutting features. Maybe I’m searching for a feature that code contracts do not have.

Answer 1

I think that what you’re looking for are called “object invariants”

From the manual, § 2.3

[ContractInvariantMethod]
private void ObjectInvariant () 
{
   Contract.Invariant ( this.y >= 0 );
   Contract.Invariant ( this.x > this.y );
}

They will be checked after each public method call.
For properly encapsulated values that should be the same as before each call.