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Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should favor polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) over inheritance from a base or parent class. [2]
Inheritance is contrasted with object composition, where one object contains another object (or objects of one class contain objects of another class); see composition over inheritance. In contrast to subtyping’s is-a relationship, composition implements a has-a relationship.
Some languages like Go do not support inheritance at all. Go states that it is object-oriented, [35] and Bjarne Stroustrup, author of C++, has stated that it is possible to do OOP without inheritance. [36] The doctrine of composition over inheritance advocates implementing has-a relationships using composition instead of inheritance. For ...
Thus in UML, composition has a more narrow meaning than the usual object composition. UML notation for association, composition and aggregation. The graphical notation represents: the property as a typed element in the box of the enclosing class, the association as a plain line between the associated classes,
In general, the further down in the hierarchy a class appears, the more specialized its behavior. When a message is sent to an object, it is passed up the inheritance tree starting from the class of the receiving object until a definition is found for the method. This process is called upcasting.
In software engineering, the delegation pattern is an object-oriented design pattern that allows object composition to achieve the same code reuse as inheritance. In delegation, an object handles a request by delegating to a second object (the delegate). The delegate is a helper object, but with the original context.
A good example of the has-a relationship is containers in the C++ STL. To summarize the relations, we have hypernym-hyponym (supertype-subtype) relations between types (classes) defining a taxonomic hierarchy, where for an inheritance relation: a hyponym (subtype, subclass) has a type-of (is-a) relationship with its hypernym (supertype ...
Design Patterns: Elements of Reusable Object-Oriented Software (1994) is a software engineering book describing software design patterns.The book was written by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, with a foreword by Grady Booch.