Broader Impact On Software Engineering
Even beyond the connection with design by contract, CQS is considered by its adherents to have a simplifying effect on a program, making its states (via queries) and state changes (via commands) more comprehensible in a manner reminiscent of how Edsger Dijkstra's admonition against gotos did the same for control flow.
CQS is well-suited to the object-oriented methodology, but can also be applied outside of object-oriented programming. There is nothing inherently object-oriented about the separation of side effects and return values, and so CQS can be profitably applied to any programming paradigm that requires reasoning about side effects.
Read more about this topic: Command-query Separation
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