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(C++) Invariant

An invariant is something that is assumed to be true. For example, the sole integer member variable of a class called 'OddIntegerNumber' can reasonably be assumed to be an odd number.

Advice

• Let a constructor establish an invariant, and throw if it cannot [1]
• Use RAII and exception handlers to maintain invariants [2]
• Design your error-handling strategy around invariants [3]
• Use PODs only when it really is just data and no invariant is meaningful for the data members [4]

Reference

1. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 13.7. Advice. page 387: '[11] Let a constructor establish an invariant, and throw if it cannot'
2. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 13.7. Advice. page 387: '[18] Use "Resource Acquisition Is Initialization" and exception handlers to maintain invariants'
3. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 13.7. Advice. page 387: '[20] Design your error-handling strategy around invariants'
4. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 16.4. Advice. page 479: '[3] Use public data (structs) only when it really is just data and no invariant is meaningful for the data members'

Go back to Richel Bilderbeek's C++ page.

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