Reading the paragraph about "illegal states" that should be avoided in software, I thought of "design by contract", what never really took off. Microsoft .NET h

Reading the paragraph about "illegal states" that should be avoided in software, I thought of "design by contract", what never really took off. Microsoft .NET has a really nice implementation called "code contracts", but it doesn't seem to be used that often. However it would be a simple and powerful way to improve the software quality.