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In computer science, an instance is an occurrence of a software element that is based on a type definition. When created, an occurrence is said to have been instantiated , and both the creation process and the result of creation are called instantiation .
Objects can contain other objects in their instance variables; this is known as object composition. For example, an object in the Employee class might contain (either directly or through a pointer) an object in the Address class, in addition to its own instance variables like "first_name" and "position".
Instance variables are properties of that object. All instances of a class have their own copies of instance variables, even if the value is the same from one object to another. One class instance can change values of its instance variables without affecting all other instances. A class may have both instance variables and class variables.
In object-oriented programming, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance. It is one of the well-known "Gang of Four" design patterns, which describe how to solve recurring problems in object-oriented software. [1]
/*Ruby has three member variable types: class, class instance, and instance. */ class Dog # The class variable is defined within the class body with two at-signs # and describes data about all Dogs *and* their derived Dog breeds (if any) @@sniffs = true end mutt = Dog. new mutt. class. sniffs #=> true class Poodle < Dog # The "class instance variable" is defined within the class body with a ...
As an instance of a class, an object is constructed from a class via instantiation. Memory is allocated and initialized for the object state and a reference to the object is provided to consuming code. The object is usable until it is destroyed – its state memory is de-allocated.
In software development, an object is an entity that has state, behavior, and identity. [ 1 ] : 78 An object can model some part of reality or can be an invention of the design process whose collaborations with other such objects serve as the mechanisms that provide some higher-level behavior.
When a member function is called on an object, it invokes the member function with the same name on the object's class object, with the object automatically bound to the first argument of the function. Thus, the obligatory first parameter of instance methods serves as this; this parameter is conventionally named self, but can be named anything.