Reading List Key Takeaways Default interface methods are included in a new feature proposal for C 8, which will allow developers to use the traits programming technique. Traits are object-oriented programming technology that promotes the reuse of methods between unrelated classes. C Addresses the diamond inheritance problem that can occur with default interface methods by taking the most specific override at runtime.
Overview[ edit ] The Abstract Factory  design pattern is one of the twenty-three well-known GoF design patterns that describe how to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.
The Abstract Factory design pattern solves problems like: How can an application be independent of how its objects are created? How can a class be independent of how the objects it requires are created? How can families of related or dependent objects be created? Creating objects directly within the class that requires the objects is inflexible because it commits the class to particular objects and makes it impossible to change the instantiation later independently from without having to change the class.
It stops the class from being reusable if other objects are required, and it makes the class hard to test because real objects can't be replaced with mock objects. The Abstract Factory design pattern describes how to solve such problems: Encapsulate object creation in a separate factory object.
That is, define an interface AbstractFactory for creating objects, and implement the interface. A class delegates object creation to a factory object instead of creating objects directly.
This makes a class independent of how its objects are created which concrete classes are instantiated. A class can be configured with a factory object, which it uses to create objects, and even more, the factory object can be exchanged at run-time. See also the UML class and sequence diagram below.
Definition[ edit ] The essence of the Abstract Factory Pattern is to "Provide an interface for creating families of related or dependent objects without specifying their concrete classes.
However, the factory only returns an abstract pointer to the created concrete object. This insulates client code from object creation by having clients ask a factory object to create an object of the desired abstract type and to return an abstract pointer to the object.
However, the type of a concrete object and hence a concrete factory is known by the abstract factory; for instance, the factory may read it from a configuration file.
The client has no need to specify the type, since it has already been specified in the configuration file. In particular, this means: The client code has no knowledge whatsoever of the concrete typenot needing to include any header files or class declarations related to it.
The client code deals only with the abstract type. Objects of a concrete type are indeed created by the factory, but the client code accesses such objects only through their abstract interface. The different factory then creates objects of a different concrete type, but still returns a pointer of the same abstract type as before — thus insulating the client code from change.
This is significantly easier than modifying the client code to instantiate a new type, which would require changing every location in the code where a new object is created as well as making sure that all such code locations also have knowledge of the new concrete type, by including for instance a concrete class header file.
If all factory objects are stored globally in a singleton object, and all client code goes through the singleton to access the proper factory for object creation, then changing factories is as easy as changing the singleton object. Instead, the Client refers to the AbstractFactory interface for creating objects, which makes the Client independent of how the objects are created which concrete classes are instantiated.
The UML sequence diagram shows the run-time interactions: What implementation of Button is returned depends on which implementation of GUIFactory is handling the method call.
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Used to write trace messages while the test is running. public abstract void WriteLine (string format, params object args); abstract member WriteLine: string * obj -> unit.
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It is available to download on this page. Use the abstract modifier in a method or property declaration to indicate that the method or property does not contain implementation. Abstract methods have the following features: An abstract method is implicitly a virtual method.