Editing Class (computer programming) (section)

=== <span class="anchor" id="PROPERTY"></span>Structure ===
[[File:oop-uml-class-example.png|frame|right|[[Unified Modeling Language|UML]] notation for classes]]

A class contains [[Data (computing)|data]] [[Field (computer science)|field]] descriptions (or ''[[property (programming)|properties]]'', ''[[field (computer science)|fields]]'', ''data [[member variable|members]]'', or ''[[attribute (computing)|attributes]]''). These are usually field types and names that will be associated with state variables at program run time; these state variables either belong to the class or specific instances of the class. In most languages, the structure defined by the class determines the layout of the memory used by its instances. Other implementations are possible: for example, objects in [[Python (programming language)|Python]] use associative key-value containers.<ref name="pythondata model">{{cite web|url=https://docs.python.org/reference/datamodel.html|title=3. Data model|work=The Python Language Reference|publisher=Python Software Foundation|access-date=2012-04-26}}</ref>

Some programming languages such as Eiffel support specification of [[class invariant|invariant]]s as part of the definition of the class, and enforce them through the type system. [[Encapsulation (object-oriented programming)|Encapsulation]] of state is necessary for being able to enforce the invariants of the class.