Creating dynamic classes

By default, the properties and methods of a class are fixed. That is, an instance of a class can't create or access properties or methods that weren't originally declared or defined by the class. For example, consider a Person class that defines two properties, name and age:

class Person {
  var name:String;
  var age:Number;
}

If, in another script, you create an instance of the Person class and try to access a property of the class that doesn't exist, the compiler generates an error. For example, the following code creates a new instance of the Person class (a_person) and then tries to assign a value to a property named hairColor, which doesn't exist.

var a_person:Person = new Person();
a_person.hairColor = "blue"; // compiler error

This code causes a compiler error because the Person class doesn't declare a property named hairColor. In most cases, this is exactly what you want to happen.

In some cases, however, you might want to add and access properties or methods of a class at runtime that aren't defined in the original class definition. The dynamic class modifier lets you do just that. For example, the following code adds the dynamic modifier to the Person class discussed previously:

dynamic class Person {
  var name:String;
  var age:Number;
}

Now, instances of the Person class can add and access properties and methods that aren't defined in the original class.

var a_person:Person = new Person();
a_person.hairColor = "blue"; // no compiler error because class is dynamic

Subclasses of dynamic classes are also dynamic.