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For example, files are provided by the operating system (specifically the file system), which in many systems represents open files with a file descriptor (an integer representing the file). These handles can be used directly, by storing the value in a variable and passing it as an argument to functions that use the resource.
For example, there is no way to give a function a pointer to a Student 's grade point average and transcript without also giving that function access to all of the personal data stored in the student's Person superclass. Many modern languages, including C++ and Java, provide a "protected" access modifier that allows subclasses to access the ...
To elaborate on the above example, consider a base class with no virtual functions. Whenever the base class calls another member function, it will always call its own base class functions. When we derive a class from this base class, we inherit all the member variables and member functions that were not overridden (no constructors or destructors).
Other method combinations are provided. An example is the + method combination, where the resulting values of each of the applicable methods of a generic function are arithmetically added to compute the return value. This is used, for example, with the border-mixin for graphical objects. A graphical object may have a generic width function.
In other words, the output of C3 superclass linearization is a deterministic Method Resolution Order (MRO). In object-oriented systems with multiple inheritance, some mechanism must be used for resolving conflicts when inheriting different definitions of the same property from multiple superclasses.
If a trait requires the consuming class to provide certain methods, the trait cannot know if those methods are semantically equivalent to the trait's needs. For some dynamic languages, such as Perl, the required method can only be identified by a method name, not a full method signature, making it harder to guarantee that the required method is appropriate.
In ADO.NET, IDbCommand.CreateParameter is an example of the use of factory method to connect parallel class hierarchies. In Qt, QMainWindow::createPopupMenu Archived 2015-07-19 at the Wayback Machine is a factory method declared in a framework that can be overridden in application code.
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]