Assign to Inheritance

[Weitentaaal]

Hello ,

How should I overwrite the AssignTo() method multiple times ?

Example:

Super class

Code: Pascal  [Select][+][-]

1. procedure TElement.AssignTo(Dest: TPersistent);
2. var
3.    NewDestElem : TElement;
4. begin
5.    IF Dest is TElement then begin
6.       NewDestElem := TElement(Dest);
7.    end;
8.  
9.  
10.    //Todo
11.    //Assign Super Class Properties
12. end;
13.  

Sub class

Code: Pascal  [Select][+][-]

1. procedure TFrontWall.AssignTo(Dest: TPersistent);
2. var
3.    NewDestElem : TElement;
4. begin
5.    IF Dest is Theadwall then begin
6.       inherited AssignTo(Dest);  //---> do i have to Copy Procedure of SuperClass or can i just call the Method ?
7.  
8.       NewDestElem := TFrontWall(Dest);
9.    end;
10.  
11.    //Todo
12.    //Assign Super Class Properties AND Sub Class properties
13. end;
14.  

I don't think this will work ?

Thanks For any Reply

[Remy Lebeau]

How should I overwrite the AssignTo() method multiple times ?

I would write it like this:

Code: Pascal  [Select][+][-]

1. procedure TElement.AssignTo(Dest: TPersistent);
2. var
3.   DestElem : TElement;
4. begin
5.   if Dest is TElement then begin
6.     DestElem := TElement(Dest);
7.     // assign only TElement properties to DestElem...
8.   end
9.   else begin
10.     inherited AssignTo(Dest); // raise runtime error
11.   end;
12. end;
13.  
14. procedure TFrontWall.AssignTo(Dest: TPersistent);
15. var
16.   DestWall : TFrontWall;
17. begin
18.   inherited AssignTo(Dest); // copy TElement properties first, or raise error
19.   if Dest is TFrontWall then begin
20.     DestWall := TFrontWall(Dest);
21.     // assign only TFrontWall properties to DestWall...
22.   end;
23. end;
24.  

[Weitentaaal]

Is it necessary to call the overwritten method of the superclass again ?

Example:

Code: Pascal  [Select][+][-]

1. constructor TSuperClass.Create();
2. begin
3.    inherited Create;
4.  
5.    //Init TSuperClass Variables
6. end;
7.  
8. constructor TSubClass.Create();
9. begin
10.    inherited Create; //--> Do i have to call Superclass Create ? or just Assign the Superclass Properties here ?
11.  
12.    //Init TSubClass Variables
13. end;
14.  

[Remy Lebeau]

Is it necessary to call the overwritten method of the superclass again ?

Construction and Assignment are two different operations.  A constructor should always call the inherited constructor to let its base class initialize itself.  You should not use Assign/To() inside a constructor.