Super

Super( ...param : any )
Super : Object

Parameter	Type		Description
param	any	->	Parameter(s) to pass to the parent constructor
Result	Object	<-	Object's parent

The Super keyword allows calls to the superclass, i.e. the parent class.

Super serves two different purposes:

1. Inside a constructor code, Super is a command that allows to call the constructor of the superclass. When used in a constructor, the Super command appears alone and must be used before the This keyword is used.

• If all class constructors in the inheritance tree are not properly called, error -10748 is generated. It's 4D developer to make sure calls are valid.
• If the This command is called on an object whose superclasses have not been constructed, error -10743 is generated.
• If Super is called out of an object scope, or on an object whose superclass constructor has already been called, error -10746 is generated.

// inside myClass constructor
var $text1; $text2 : Text
Super($text1) //calls superclass constructor with a text param
This.param:=$text2 // use second param

2. Inside a class function, Super designates the prototype of the superclass and allows to call a function of the superclass hierarchy.

Super.doSomething(42) //calls "doSomething" function  
//declared in superclasses

Example 1

This example illustrates the use of Super in a class constructor. The command is called to avoid duplicating the constructor parts that are common between Rectangle and Square classes.

// Class: Rectangle
Class constructor($width : Integer; $height : Integer)
 This.name:="Rectangle"
 This.height:=$height
 This.width:=$width


Function sayName()
 ALERT("Hi, I am a "+This.name+".")

// Function definition
Function getArea() : Integer

 return (This.height)*(This.width)

//Class: Square

Class extends Rectangle

Class constructor ($side : Integer)

 // It calls the parent class's constructor with lengths
 // provided for the Rectangle's width and height
 Super($side;$side)
 // In derived classes, Super must be called 
 // before you can use 'This'
 This.name:="Square"

Function getArea() : Integer
 return This.height*This.width

Example 2

This example illustrates the use of Super in a class function. You created the Rectangle class with a function:

//Class: Rectangle

Function nbSides() : Text
 return "I have 4 sides"

You also created the Square class with a function calling the superclass function:

//Class: Square

Class extends Rectangle

Function description() : Text
  return Super.nbSides()+" which are all equal"

Then you can write in a project method:

var $square : Object
var $message : Text
$square:=cs.Square.new()
$message:=$square.description() //I have 4 sides which are all equal

See also

Concept page for Classes.

Properties

Command number	1706
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