Weird Inheritance error

Monkey Forums/Monkey Programming/Weird Inheritance error

Vinians

(Posted 2013) [#1]

I´m getting this error
<quote>
Unable to find overload for new(Int,Int,Int).
</quote>
When trying to create an object from child class... see an example:

Class TActor extends Object
   Method New()
   end
   Method New(a:int, b:int = 0, c:int = 0)
   End
   Method OnOutsideRoom()
   End
End
Class Fire extends TActor
   Method OnOutsideRoom()
      PleaseDestroyMe()
   End
End

Function Main:int()

  Local in:Fire = new Fire(TActor.TYPE_ELLIPSE, 5, 5) //error here!     
End

Why ? This is just an example to illustrate the problem, the real class is bigger and tested, just now when I tryed to extend it I got this error. Do I need to recreate the constructor ? Isen´t it inherited from its father?
Thanks!

computercoder

(Posted 2013) [#2]

It is not inherited as you'd think, but you will need to call each overload you want the child to expose from within the child class.

You need to add Super.New() as the first line to each of the overloads in the child class matching the parent class. This will instantiate the base class's overloaded constructors as expected.

Here's an updated example:

Import mojo
Import monkey

Class TActor Extends Object
   Method New()
   End
   Method New(a:Int, b:Int = 0, c:Int = 0)
   End
   Method OnOutsideRoom()
   End
End
Class Fire extends TActor
   Method New()
     Super.New()
   End
   Method New(a:Int, b:Int = 0, c:Int = 0)
     Super.New(a,b,c)
   End
   Method OnOutsideRoom()
   End
   Method OnOutsideRoom()
      PleaseDestroyMe()
   End
End

Function Main:int()

  Local in:Fire = New Fire(0, 5, 5) 'error here!     
End

Vinians

(Posted 2013) [#3]

So, constructors are NOT inherited from base class like other methods? It Means that all derivate class needs to create a constructor just to call father's one?

computercoder

(Posted 2013) [#4]

Yes. It seems strange, I know, but this is the only way I've been able to get a child class to instantiate using the parent constructor.

ziggy

(Posted 2013) [#5]

If I'm not wrong, New() is called from inheritance order, and overloads have to be declared on each class:

Function Main()
	New MyClass3
End

Class MyClass1
	Method New()
		Print "MyClass1 New"
	End
End

Class MyClass2 Extends MyClass1
	Method New()
		Print "MyClass2 New"
	End
End


Class MyClass3 Extends MyClass2
	Method New()
		Print "MyClass3 New"
	End	
End

This outputs:

MyClass1 New
MyClass2 New
MyClass3 New

So all important initialization code that needs to be inherited, should be placed on the parameterless New methods. Then overloads for this method should be defined in a per-class basis. Any class can add any number of overloads here at any point of the inheritance tree.