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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 ...
Objects are instances of a class. Object-oriented programming (OOP) is a programming paradigm based on the concept of objects, [1] which can contain data and code: data in the form of fields (often known as attributes or properties), and code in the form of procedures (often known as methods).
A language that supports creating an object from a class is classified as class-based. A language that supports object creation via a template object is classified as prototype-based. The concept of object is used in many different software contexts, including: Possibly the most common use is in-memory objects in a computer program written in ...
In knowledge representation, particularly in the Semantic Web, a metaclass is a class whose instances can themselves be classes. Similar to their role in programming languages, metaclasses in ontology languages can have properties otherwise applicable only to individuals, while retaining the same class's ability to be classified in a concept hierarchy.
The object methods include access to the object state (via an implicit or explicit parameter that references the object) whereas class methods do not. If the language supports inheritance , a class can be defined based on another class with all of its state and behavior plus additional state and behavior that further specializes the class.
A metaobject protocol (MOP) provides the vocabulary to access and manipulate the structure and behaviour of systems of objects. Typical functions of a metaobject protocol include: [2] Create or delete a new class; Create a new property or method; Cause a class to inherit from a different class ("change the class structure")
In class-based programming, a factory is an abstraction of a constructor of a class, while in prototype-based programming a factory is an abstraction of a prototype object. A constructor is concrete in that it creates objects as instances of one class, and by a specified process (class instantiation), while a factory can create objects by instantiating various classes, or by using other ...
A reference to an instance of a class may actually be referring to one of its subclasses. The actual class of the object being referenced is impossible to predict at compile-time. A uniform interface is used to invoke the member functions of objects of a number of different classes.