Nested Classes and Scope

[syntonica]

I'm having an argument with nested classes. They're not working how I'm telling them to work, and I pay my classes well! 

Here is my example:

Code: Pascal  [Select][+][-]

1. {$mode objfpc}
2. program test6;
3.  
4. type
5.   Class1 = class
6.     type
7.       Class2 = class
8.         procedure find;
9.       end;
10.     var
11.       b: Class2;
12.       ICanSeeYou: Boolean;
13.   end;
14.  
15. procedure Class1.Class2.find;
16.   begin
17.     if ICanSeeYou then WriteLn('Found you!') else WriteLn('Where are you?');  //Fails compilation!
18.   end;
19.  
20. var
21.   a: Class1;
22.  
23. begin
24.   a := Class1.Create;
25.   a.ICanSeeYou := True;
26.   a.b := a.Class2.Create;
27.   a.b.find;
28. end.
29.  

Currently "ICanSeeYou" is not in Class2's scope. Is there any way to solve this other than passing my Class1 instance explicitly?  Making 'ICanSeeYou' static is not an option.

[marcov]

No. Inner classes and their parents work like any other two classes in this regard.

[syntonica]

Meh. No point in nesting then...


Looks like I'll have to pass the pointer. 


Thanks!

[jamie]

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls;
9.  
10. type
11. Class1 = Class
12.    Type
13.     Class2 = Class
14.      fOwner :Tobject;
15.      Procedure Find;
16.      constructor Create(aOwner:Tobject);
17.     End;
18.   Var
19.   IcanSeeYou:Boolean;
20.   B:Class2;
21. end;
22.  
23.   { TForm1 }
24.  
25.   TForm1 = class(TForm)
26.     Button1: TButton;
27.     procedure Button1Click(Sender: TObject);
28.   private
29.  
30.   public
31.  
32.   end;
33.  
34. var
35.   Form1: TForm1;
36.  
37. implementation
38.  
39. {$R *.lfm}
40.  
41. { TForm1 }
42.  
43. procedure TForm1.Button1Click(Sender: TObject);
44. Var
45.   B:Class1;
46. begin
47.   B := Class1.Create;
48.   B.B := B.Class2.Create(B);
49.   B.IcanSeeYou := True;
50.   B.B.Find;
51.   B.B.Free;
52.   B.Free;
53. end;
54. Constructor Class1.Class2.Create(AOwner:Tobject);
55. Begin
56.   fOwner := AOwner;
57. end;
58.  
59. Procedure Class1.Class2.Find;
60. Begin
61.   If Class1(fOwner).ICanSeeYou  Then Form1.Caption := 'Yup';
62. End;
63.  
64. end.
65.  

Why someone would want to do this is beyond me but what ever!

[syntonica]

Code: Pascal  [Select][+][-]

1. Totally obvious answer.
2.  

Why someone would want to do this is beyond me but what ever!

Duh. I've been Pascalizing way too much these last two weeks... 

I needed a set of classes that had access to the main class's stuff. I thought there would be a some love between them, but looks like classes are their own little fiefdoms.

Anyway, y'all are most helpful, as always! Thank you!

[marcov]

Meh. No point in nesting then...
Looks like I'll have to pass the pointer. 

Not much point indeed. Only for generics there is some use (since then the nested type specializes with the mother type), otherwise I never use nested classes.

[jamie]

maybe a advanced record or Object inside would be more appropriate since then one would not need to worry about freeing it.

[marcov]

maybe a advanced record or Object inside would be more appropriate since then one would not need to worry about freeing it.

Usually the nested types in those generics are record based iterators, yes.

[Weiss]

good example above by Jamie. One thing I am still trying to get is fOwner, why do we need it, can another object claim ownership of another object's nested object? I am using word "object" as instance of class.

[Warfley]

You have access to the symbols of your parent class, but not of the instance:

Code: Pascal  [Select][+][-]

1. type
2.   TParent = class
3.   public type
4.     TChild = class
5.     public procedure Foo;
6.     end;
7.   public
8.     class procedure Bar;
9.   end;
10.  
11. procedure TParent.TChild.Foo;
12. begin
13.   Bar; // Symbol of parent class
14. end;
15.  
16. class procedure TParent.Bar;
17. begin
18.   WriteLn('Bar');
19. end;

Because the child type is a member of the class, not of the instance (if that makes sense) you only have access to class symbols