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Classes that a developer can create and the instances of which a user can create are called custom classes

Inheritance

When creating custom class B you can explicitly specify that its parent is class A. In this case, class A shall be called the parent class of class B.

A parent class of a custom class can only be another custom class. Inheriting from built-in classes is not possible. If no parent class is specified when creating a custom class, this class is implicitly inherited from the Object class (located in the System module). Thus, the System.Object class is the parent object of all custom classes.

The platform supports multiple inheritance of custom classes, meaning that a class can have several parent classes. 

Abstract classes

Some custom classes in the system can be abstract. The difference between these classes and the rest is that it is impossible to create an instance of an abstract class. Non-abstract classes, in turn, are called concrete.

Class change

The platform allows changing the class of an existing object. Since objects can only be instances of concrete classes, it is forbidden to change the class of an object to abstract.

Common ancestor

As a common ancestor for several custom classes, the platform selects a class from which all these classes are inherited, and the total number of "steps" of inheritance to these classes is minimal (that is, the closest class is selected).

Language

To add a new custom class to the system, use the CLASS instruction.

Examples

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 CLASS ABSTRACT Document; // The caption of this class will be 'Document'
CLASS IncomeDocument 'Income' : Document;
CLASS OutcomeDocument 'Expenses' : Document;
 
CLASS Person;
CLASS Worker;
CLASS Musician : Person, Worker; // multiple inheritance
 
CLASS Barcode 'Barcode'; // The parent class of Barcode will be the System.Object class
 
CLASS PrintOrientation {
    portrait 'Portrait',
    landscape 'Landscape'
}

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