[solved ] Class method inheritance doesn’t allow skipping

[Kraig]

I am making a series of classes most of which have an overriding method from the virtual method in base class, however I can’t seem to skip having a method in the most recent ancestor and have to make a dummy method in the immediate ancestor to be allowed to override it.

Here is an example

Code: Pascal  [Select][+][-]

1. A = class (tbutton)
2. Constructor create (the owner:tcomponet); override;
3. Strict protected
4. Procedure test; virtual;
5. End;
6.  
7. B = class (a)
8. Constructor create (the owner:tcomponet); override;
9. End;
10.  
11. C = class (b)
12. Constructor create (the owner:tcomponet); override;
13. Strict protected
14. Procedure test; override; // gives error that there is no ancestor method to override,
15. End
16.  
17.  

it seems like the procedure test in class a is out of scope even though it is an ancestor . Is this behavior intentional? If so why?

[Thaddy]

That is simply because you did not call inherited.

[bytebites]

Does not give any error with procedure test.

Code: Pascal  [Select][+][-]

1. program foo;
2.  
3. {$mode objfpc}
4. {$H+}
5. uses
6.   SysUtils;
7.  
8. type
9.  
10.   { A }
11.  
12.   A = class
13.     constructor Create;
14.   strict protected
15.     procedure test; virtual;
16.   end;
17.  
18.   { B }
19.  
20.   B = class(A)
21.   strict protected
22.     procedure test; override;
23.   end;
24.  
25.   { C }
26.  
27.   C = class(B)
28.     constructor Create;
29.   strict protected
30.     procedure test; override;
31.   end;
32.  
33.   { A }
34.  
35.   constructor A.Create;
36.   begin
37.  
38.   end;
39.  
40.   procedure A.test;
41.   begin
42.  
43.   end;
44.  
45.   { B }
46.  
47.   procedure B.test;
48.   begin
49.     inherited test;
50.   end;
51.  
52.   { C }
53.  
54.   constructor C.Create;
55.   begin
56.  
57.   end;
58.  
59.   procedure C.test;
60.   begin
61.     inherited test;
62.   end;
63.  
64.  
65. begin
66. end.

[PascalDragon]

Here is an example

Please provide a complete example that can be compiled. As bytebites showed, this should work (even if the B.test method from his example is removed).

[Kraig]

Sorry for all the trouble,  I believe that I have found the problem I don’t really understand why it happened though. I had a method in immediate ancestor with same name but Containing a parameter
I thought that it would be obvious that they didn’t match but it seems to only go by name instead of name with parameter. Adding overload seemed to solve it but I’m still not sure why it got confused.

Code: Pascal  [Select][+][-]

1.  
2. A = class (tbutton)
3. Constructor create (the owner:tcomponet); override;
4. Strict protected
5. Procedure test; virtual;
6. End;
7.  
8. B = class (a)
9. Constructor create (the owner:tcomponet); override;
10. Strict protected
11. Procedure test (const x:string); overload;
12. End;
13.  
14. C = class (b)
15. Constructor create (the owner:tcomponet); override;
16. Strict protected
17. Procedure test; override; // was being blocked by Procedure test (const x:string);
18. End
19.  
20.  

When I tried using virtual on procedure with same name instead of overload, it didn’t work. I guess this means that there can’t be different virtual procedures with the same name?

[ASerge]

When I tried using virtual on procedure with same name instead of overload, it didn’t work. I guess this means that there can’t be different virtual procedures with the same name?

In this case, the reintroduce directive is used.

Code: Pascal  [Select][+][-]

1. {$MODE OBJFPC}
2. type
3.   TA = class
4.   strict protected
5.     procedure Test; virtual;
6.   end;
7.  
8.   TB = class(TA)
9.   strict protected
10.     procedure Test(const X: string); overload;
11.   end;
12.  
13.   TC = class(TB)
14.   strict protected
15.     procedure Test(X: SizeInt); reintroduce;
16.   end;
17.  
18. procedure TA.Test;
19. begin
20. end;
21.  
22. procedure TB.Test(const X: string);
23. begin
24. end;
25.  
26. procedure TC.Test(X: SizeInt);
27. begin
28. end;
29.  
30. begin
31. end.

[Kraig]

Oh ? I’ve never heard of that one ..

[ASerge]

Oh ? I’ve never heard of that one ..

In my example, C.Test can also be virtual.

[Kraig]

I just tried reintroduce in place of the overload but it didn’t compile ..
ah the reintroduce is used after the overload 
I think I’ve seen reintroduce used with making new types of constructors.