Dynamic Extensions

Methods of a class, which includes methods of all objects of that class, can be replaced by methods of a dynamic extension class.

class Window
public:
    proc init(...)
      begin
      ...
      end
    proc draw()
      ..
    ..
end

// same syntax as shell classes

shell class Border(Window)
public:
    proc init()
      begin
      end
    proc draw()
      begin
      self.drawBorder();
      super.draw();
      end
private:
    proc drawBorder()
      ...
end

The previous code defines a dynamic extension class Border (or just extension Border) that is attached to a class Window by command

Meta.attachExtension(Window, Border)

The syntax for dynamic extension classes is the same for shell classes.

An extension is removed by

Meta.removeExtension(Window)

A complete example of the use of extensions is below.

var w1, w2 : Window;

w1 = Window.new(...);
w2 = Window.new(...);
// draw windows without borders
w1.draw();
w2.draw();

Meta.attachExtension( Window, Border );

// draw windows with borders
w1.draw();
w2.draw();

var catch : CatchMetaException;

catch#init();
try(catch)
Meta.removeExtension(Window);
// draw windows without borders
w1.draw();
w2.draw();
end

What is new ?

The advantages of dynamic extensions are similar to those of shells: they are easy to understand and efficient. Besides that, we only know one statically type language that allows one change the methods of a whole class: Meta Java. Method interceptAll of shells can also be used with dynamic extensions.

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