How Invariant are Invariants?

Class invariants are a vital tool when writing robust code. Classes are easier to use and easier to maintain if you know that some conditions are always true. But C++ makes it impossible to maintain invariants in all cases. We will look at a simple class with a seemingly simple invariant. Then we'll discover why that class is impossible to implement correctly and explore techniques for dealing with the situation. You will come away with new insights on class invariants and guidelines for writing and using classes in robust code.