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Together this implies that a class in Smalltalk is an object and that, therefore a class needs to be an instance of a class (called metaclass). As an example, a car object c is an instance of the class Car. In turn, the class Car is again an object and as such an instance of the metaclass of Car called Car class. Note the blank in the name of ...
Before a class derived from an abstract class can be instantiated, all abstract methods of its parent classes must be implemented by some class in the derivation chain. [ 25 ] Most object-oriented programming languages allow the programmer to specify which classes are considered abstract and will not allow these to be instantiated.
In computer science, a container is a class or a data structure [1] [2] whose instances are collections of other objects. In other words, they store objects in an organized way that follows specific access rules. The size of the container depends on the number of objects (elements) it contains.
In class-based object-oriented programming, abstract types are implemented as abstract classes (also known as abstract base classes), and concrete types as concrete classes. In generic programming , the analogous notion is a concept , which similarly specifies syntax and semantics, but does not require a subtype relationship: two unrelated ...
Modern object-oriented languages, such as C++ and Java, support a form of abstract data types. When a class is used as a type, it is an abstract type that refers to a hidden representation. In this model, an ADT is typically implemented as a class, and each instance of the ADT is usually an object of that class.
The messages that flow between computers to request services in a client-server environment can be designed as the linearizations of objects defined by class objects known to both the client and the server. For example, a simple linearized object would consist of a length field, a code point identifying the class, and a data value.
C appears to support assignment of array pointers, but in fact these are simply pointers to the array's first element, and again do not carry the array's size. [citation needed] In most languages, data types are not first-class objects, though in some object-oriented languages, classes are first-class objects and are instances of metaclasses.
Each class is an instance of the metaclass of that class. Metaclasses in turn are also objects, and are all instances of a class named Metaclass. Classes contain method dictionaries that map selectors (the equivalent of function procedure names in other languages) to method objects, objects that are executed to evaluate messages.