Command-query separation

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Command-Query-Separation ( CQS , English for command-query separation ) is a principle of software design . The CQS principle wasconceivedby Bertrand Meyer in the course of his work on the Eiffel programming language .

The CQS principle states that a method either as a query ( query ) or as a command ( command , modifier or mutator ) is to be implemented. A query must return data and must not have any side effects on the observable state of the system, while a command has observable side effects and does not return any data.

See also

swell

  1. ↑ Martin Fowler: command-query separation. December 5, 2005, accessed May 18, 2014 .
Principles of object-oriented design


SOLID principles

Single Responsibility  • Open Closed  • Liskov Substitution Principle  • Interface Segregation  • Dependency Inversion

Further principles

Demeter's law  • Design by contract  • Data encapsulation  • Linguistic Modular Units  • Self-Documentation  • Uniform Access  • Single Choice  • Persistence Closure  • Command Query Separation  • Principle of Least Surprise

Packaging principles

Reuse Release Equivalence  • Common Closure  • Common Reuse  • Acyclic Dependencies  • Stable Dependencies  • Stable Abstractions