Editing Class (computer programming) (section)

===Type===

An object expresses [[data type]] as an interface {{endash}} the type of each member variable and the signature of each [[member function]] (method). A class defines an implementation of an interface, and instantiating the class results in an object that exposes the implementation via the interface.{{sfn|Gamma|Helm|Johnson|Vlissides|1995|p=17}} In the terms of type theory, a class is an implementation{{mdashb}}a ''concrete'' [[data structure]] and collection of subroutines{{mdashb}}while a type is an [[Protocol (object-oriented programming)|interface]]. Different (concrete) classes can produce objects of the same (abstract) type (depending on type system). For example, the type (interface) {{Mono|Stack}} might be implemented by {{Mono|SmallStack}} that is fast for small stacks but scales poorly and {{Mono|ScalableStack}} that scales well but has high overhead for small stacks.