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[26] [27] In C++, an abstract class is a class having at least one abstract method given by the appropriate syntax in that language (a pure virtual function in C++ parlance). [25] A class consisting of only pure virtual methods is called a pure abstract base class (or pure ABC) in C++ and is also known as an interface by users of the language. [13]
Abstract data type for an abstract description of a set of data; Algorithm for an abstract description of a computational procedure; Bracket abstraction for making a term into a function of a variable; Data modeling for structuring data independent of the processes that use it; Encapsulation for abstractions that hide implementation details
A class containing a pure virtual function is called an abstract class. Objects cannot be created from an abstract class; they can only be derived from. Any derived class inherits the virtual function as pure and must provide a non-pure definition of it (and all other pure virtual functions) before objects of the derived class can be created.
The bridge pattern is useful when both the class and what it does vary often. The class itself can be thought of as the abstraction and what the class can do as the implementation. The bridge pattern can also be thought of as two layers of abstraction. When there is only one fixed implementation, this pattern is known as the Pimpl idiom in the ...
An abstract method is one with only a signature and no implementation body. It is often used to specify that a subclass must provide an implementation of the method, as in an abstract class. Abstract methods are used to specify interfaces in some programming languages. [6]
The C++ examples in this section demonstrate the principle of using composition and interfaces to achieve code reuse and polymorphism. Due to the C++ language not having a dedicated keyword to declare interfaces, the following C++ example uses inheritance from a pure abstract base class.
For example, class UnicodeConversionMixin might provide a method unicode_to_ascii() when included in class FileReader and class WebPageScraper, which do not share a common parent. Abstract classes cannot be instantiated into objects; they exist only for inheritance into other "concrete" classes that can be instantiated.
Any call to a class (static or constructor call), triggers the static constructor execution. Static constructors are thread safe and implement a singleton pattern. When used in a generic programming class, static constructors are called at every new generic instantiation one per type. [8]: 38 [4]: 111 Static variables are instantiated as well.