Law of Demeter
The Law of Demeter is a design principle that limits a component’s knowledge of and interaction with other components’ internal structure.
Object-Oriented Software Design in C++
The Law of Demeter is a software design principle that limits how much implementation knowledge and object-structure navigation a component exposes or relies upon.
- How it is used
- Guides class design toward loose coupling by limiting dependencies on other objects’ implementations.
- How deep it goes
- Defines four legal call relationships and connects them to private members, encapsulation, and change isolation.
- Examples
- Uses C++ classes named DemeterAuto, Engine, and Sparkplug to contrast direct calls with returned-object navigation.
- What you can do after
- Apply it to expose necessary behavior while avoiding calls through objects returned by other objects.
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Software Design for Python Programmers
The Principle of Least Knowledge is a design principle that minimizes a class's knowledge of other classes' implementations and thereby reduces dependencies between classes.
- How it is used
- Guides class design toward hidden implementations, loose coupling, and changes that remain localized.
- How deep it goes
- Defines four method-call rules and demonstrates their consequences, but stops short of formal metrics for coupling.
- Examples
- Uses Catalogue, Attributes, Book, DemeterAuto, Engine, and Sparkplug examples to contrast delegation with chained access.
- What you can do after
- Evaluate method calls for problematic object reach-through and design narrower public operations that preserve implementation freedom.
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Related concepts
- couplinguses · Coupling is the degree of dependency between software components, including how their behavior, availability, or changes affect one another.
- encapsulationuses · Encapsulation is a software design principle that contains state and implementation details behind a controlled interface, limiting direct access from outside.
- dependencyaddresses · A software dependency is a component, resource, or prerequisite on which another software component or operation relies to function or proceed.
- compositionuses · Composition is a technique for combining simpler functions, components, or operations into a larger structure or behavior.
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