Classes and Instances

Terminology Summary
class An object that describes the implementation of a set of similar objects.
instance One of the objects described by a class; it has memory and responds to messages.
instance variable A variable available to a single object for the entire lifetime of the object; instance variables can be named or indexed.
protocal description A description of a class in terms of its instances public message protocal.
implementation description A message selector and a set of argument names, one for each argument that a message with this selector must have.
temporary variable A variable created for a specific activity and available only for the duration of that activity.
class variable A variable shared by all the instances of a single class.
global variable A variable shared by all the instances of all classes.
pool variable A variable shared by the instances of a set of classes.
Smalltalk A pool shared by all classes that contains the global variables.
method A procedure describing how to perform one of an object’s operations; it is made up of a message pattern, temporary variable declaration, and a sequence of expressions. A method is executed when a message matching its message pattern is sent to an instance of the class in which the method is found.
argument name Name of a pseudo-variable available to a method only for the duration of that method’s execution; the value of the argument names are the arguments of the message that invoked the method.
up When used in a method, indicates that the value of the next expression is to be the value of the method.
self A pseudo-variable referring to the receiver of a message.
message category A group of methods in a class description.
primitive method An operation performed directly by the Smalltalk-80 virtual machine; it is not described as a sequence of Smalltalk-80 expressions.