RosettaCodeData/Task/Classes/00DESCRIPTION

In [[object-oriented programming]] '''class''' is a set (a [[wp:Transitive_closure|transitive closure]]) of types bound by the relation of [[inheritance]]. It is said that all types derived from some base type T and the type T itself form a class T.

The first type T from the class T sometimes is called the '''root type''' of the class.

A class of types itself, as a type, has the values and operations of its own.
The operations of are usually called '''methods''' of the root type.
Both operations and values are called [[polymorphism | polymorphic]].

A polymorphic operation (method) selects an implementation depending on the actual specific type of the polymorphic argument.

The action of choice the type-specific implementation of a polymorphic operation is called '''dispatch'''. Correspondingly, polymorphic operations are often called '''dispatching''' or '''virtual'''.
Operations with multiple arguments and/or the results of the class are called '''multi-methods'''.
A further generalization of is the operation with arguments and/or results from different classes.

* single-dispatch languages are those that allow only one argument or result to control the dispatch. Usually it is the first parameter, often hidden, so that a prefix notation ''x''.''f''() is used instead of mathematical ''f''(''x'').
* multiple-dispatch languages allow many arguments and/or results to control the dispatch.

<br>
A polymorphic value has a type tag indicating its specific type from the class and the corresponding specific value of that type.
This type is sometimes called '''the most specific type''' of a [polymorphic] value.
The type tag of the value is used in order to resolve the dispatch.
The set of polymorphic values of a class is a transitive closure of the sets of values of all types from that class.

In many [[object-oriented programming | OO]] languages
the type of the class of T and T itself are considered equivalent.
In some languages they are distinct (like in [[Ada]]).
When class T and T are equivalent, there is no way to distinguish
polymorphic and specific values.


;Task:
Create a basic class with a method, a constructor, an instance variable and how to instantiate it.
<br><br>