Versioning

Versioning Contracts, Not Just Releases

A version number is useful only when its consumers can make a decision from it. Suppose a library changes from 2.4.1 to 2.5.0. A developer considering the upgrade wants to know something practical: can existing code keep working, or must it change? The answer does not come from how much code the maintainer edited. It comes from whether the release changed a contract that consumers depend on. That contract includes more than function names. It can include accepted inputs, returned values, error behavior, configuration, file formats, command-line options, extension points, and other observable behavior that the project promises to preserve.