Super
Super {( param {; param2 ; ... ; paramN} )} -> Function result
| Parameter | Type | Description | |
|---|---|---|---|
| param | Mixed | 🡒 | Parameter(s) to pass to the parent constructor |
| Function result | Object | 🡐 | Object's parent |
Description
The Super command makes calls to the superclass.
Super has been introduced to serve two different purposes:
- 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 $1;$2 : Text
Super($1) //calls superclass constructor with a text param
This.param:=$2 // use second param
- inside a class member 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
var $1;$2 : Integer
This.name:="Rectangle"
This.height:=$1
This.width:=$2
Function sayName
ALERT("Hi, I am a "+This.name+".")
Function getArea
var $0 : Integer
$0:=This.height*This.width
//Class: Square
Class extends Rectangle
Class constructor
var $1 : Integer
// It calls the parent class's constructor with lengths
// provided for the Rectangle's width and height
Super($1;$1)
// In derived classes, Super must be called before you
// can use 'This'
This.name:="Square"
Example 2
This example illustrates the use of Super in a class member method.
You created the Rectangle class with a function:
//Class: Rectangle
Function nbSides
var $0 : Text
$0:="I have 4 sides"
You also created the Square class with a function calling the superclass function:
//Class: Square
Class extends Rectangle
Function description
var $0 : Text
$0:=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