In object-oriented programming class is a set (a 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  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.


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  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.




class Car 
{
  //Constructor function.
  function this(brand, weight, price = 0) {
    this.brand = brand;
    this.weight = weight || 1000; // Resort to default value (with 'or' notation).
    this._price = price;
  }
  property price(v) // computable property, special kind of member function
  {
    get { return this._price; } // getter section 
    set { this._price = v; }    // setter section
  }
  function toString() { // member function, method of a Car.
    return String.printf("<%s>",this.brand);
  }
}
 
class Truck : Car 
{
  function this(brand, size) {
    super(brand, 2000); // Call of constructor of super class (Car here)
    this.size = size; // Custom property for just this object.
  }
}
 
var cars = [ // Some example car objects.
  new Car("Mazda"),
  new Truck("Volvo", 2, 30000)
];
for (var (i,car) in cars) // TIScript allows enumerate indexes and values
{
  stdout.printf("#%d %s $%d %v %v, %v %v", i, car.brand, car.price, car.weight, car.size,
                 car instanceof Car, car instanceof Truck);
}