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Some object-oriented languages, such as Swift, Java, Fortran since its 2003 revision, C#, and Ruby implement single inheritance, although protocols, or interfaces, provide some of the functionality of true multiple inheritance. PHP uses traits classes to inherit specific method implementations. Ruby uses modules to inherit multiple methods.
In languages supporting multiple inheritance, such as C++, interfaces are implemented as abstract classes. In languages without explicit support, protocols are often still present as conventions. This is known as duck typing. For example, in Python, any class can implement an __iter__ method and be used as a collection. [3]
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]
Not all languages support multiple inheritance. For example, Java allows a class to implement multiple interfaces, but only inherit from one class. [22] If multiple inheritance is allowed, the hierarchy is a directed acyclic graph (or DAG for short), otherwise it is a tree. The hierarchy has classes as nodes and inheritance relationships as links.
implement the interface of the extended (decorated) object (Component) transparently by forwarding all requests to it. perform additional functionality before or after forwarding a request. This allows working with different Decorator objects to extend the functionality of an object dynamically at run-time.
During the 1990s, the open–closed principle became popularly redefined to refer to the use of abstracted interfaces, where the implementations can be changed and multiple implementations could be created and polymorphically substituted for each other. In contrast to Meyer's usage, this definition advocates inheritance from abstract base ...
Multiple inheritance where one class can have more than one superclass and inherit features from all parent classes. "Multiple inheritance ... was widely supposed to be very difficult to implement efficiently. For example, in a summary of C++ in his book on Objective C, Brad Cox actually claimed that adding multiple inheritance to C++ was ...
The g++ compiler implements the multiple inheritance of the classes B1 and B2 in class D using two virtual method tables, one for each base class. (There are other ways to implement multiple inheritance, but this is the most common.) This leads to the necessity for "pointer fixups", also called thunks, when casting. Consider the following C++ code: