[SOLVED]Diferences in Generics in mode FPC or Delphi

[janasoft]

Hello.
Next code compile and work correctly

Code: Pascal  [Select][+][-]

1. {$APPTYPE CONSOLE}
2. {$mode Delphi}
3.  
4. program project1;
5.  
6. uses generics.collections;
7.  
8. type
9.   TEntity= class
10.   ID: integer;
11.   end;
12.  
13.   TInheritedEntity = class(TEntity)
14.   Name: string
15.   end;
16.  
17.   TEntityList = TObjectList <TEntity>;
18.   TInheritedEntityList = TObjectList <TInheritedEntity>;
19.  
20.    TSubject = class
21.     EntityList: TEntityList;
22.   end;
23.  
24.    TInheritedSubject = class (TSubject)
25.     EntityList: TInheritedEntityList;
26.   end;
27.  
28.   var subject: TSubject;
29.       inheritedSubject: TInheritedSubject;
30.       ent: TEntity;
31.       inheritedEnt: TInheritedEntity;
32.  
33. begin
34.   ent:= TEntity.Create;
35.   ent.ID:=0;
36.   inheritedEnt:= TInheritedEntity.Create;
37.   inheritedEnt.ID:=1;
38.   inheritedEnt.Name:='Entity';
39.  
40.   subject:= TSubject.create;
41.   subject.EntityList:=TEntityList.Create;
42.  
43.   inheritedSubject:= TInheritedSubject.create;
44.   inheritedSubject.EntityList:=TInheritedEntityList.Create;
45.  
46.   subject.EntityList.Add(ent);
47.   inheritedSubject.EntityList.Add(inheritedEnt);
48.  
49.   writeln(subject.EntityList.Items[0].ClassName);
50.   writeln(subject.EntityList.Items[0].ID);
51.   writeln(inheritedSubject.EntityList.Items[0].ClassName);
52.   writeln(inheritedSubject.EntityList.Items[0].ID);
53.   writeln(inheritedSubject.EntityList.items[0].Name);
54.   writeln; write('type enter'); Readln;
55.  
56.   subject.EntityList.free;
57.   subject.Free;
58.   inheritedSubject.EntityList.Free;
59.   inheritedSubject.Free;
60. end.                  

But if i try the same code with FP Generics

Code: Pascal  [Select][+][-]

1. {$APPTYPE CONSOLE}
2. {$mode ObjFPC}
3.  
4. program project1;
5.  
6.  uses  fgl;
7.  
8.  type
9.    TEntity= class
10.    ID: integer;
11.    end;
12.  
13.    TInheritedEntity = class(TEntity)
14.    Name: string
15.    end;
16.  
17.    TEntityList = specialize TFPGObjectList <TEntity>;
18.    TInheritedEntityList = specialize TFPGObjectList <TInheritedEntity>;
19.  
20.    TSubject = class
21.      EntityList: TEntityList;
22.    end;
23.  
24.    TInheritedSubject = class (TSubject)
25.      EntityList: TInheritedEntityList;
26.    end;
27.  
28.    var subject: TSubject;
29.        inheritedSubject: TInheritedSubject;
30.        ent: TEntity;
31.        inheritedEnt: TInheritedEntity;      

I get the error: Duplicate identifier "EntityList"

I supose that I am doing something wrong or is this the way it has to work?

Regards

Lazarus 2.2.6 (rev lazarus_2_2_6) FPC 3.2.2 x86_64-win64-win32/win64

[jamie]

maybe put this at the top ?

{$modeSwitch DUPLICATELOCALS}

[janasoft]

Many thanks for your answer jamie but I get the same error

[bytebites]

Change to delphi-mode

[cdbc]

Hi
You've defined:

Code: Pascal  [Select][+][-]

1.    TSubject = class
2.     EntityList: TEntityList;
3.   end;
4.  
5.    TInheritedSubject = class (TSubject)
6.     EntityList: TInheritedEntityList;
7.   end;

without visibility specifier and by convention they're then "public" / "published" depending on {$M+/-}
That means you WILL have a duplicate identifier. You could put EntityList in "private" then they can't see eachother, but if it's a solution for you, I dunno...
edit: in different units they can't see eachother...
Regards Benny

[marcov]

I'm usually not a defender of $mode objfpc, but in this case I think it is right, having a class with two different (and differently typed) entitylist fields is a mess.

[janasoft]

Hello and first of all, thanks for your answers.

Change to delphi-mode

@bytebites In Delphi mode works correctly. The question is exactly that. Why works correctly in Delphi Mode and fails in FPC mode? What's the difference between both modes?

That means you WILL have a duplicate identifier. You could put EntityList in "private" then they can't see eachother, but if it's a solution for you, I dunno...
edit: in different units they can't see eachother...
Regards Benny

@cdbc I've made this change

Code: Pascal  [Select][+][-]

1.    TSubject = class
2.    strict private
3.      FEntityList: TEntityList;
4.      procedure SetEntityList(AValue: TEntityList);
5.    public
6.      property EntityList:TEntityList read FEntityList write SetEntityList;
7.    end;

Now  theres is no problem at the moment of declare the variables, but now I get the error 'Incompatible type for arg no. 1: Got "TFPGObjectList<project1.TInheritedEntity>", expected "TFPGObjectList<project1.TEntity>".
So I think it is not an issue of visibility but of type assigning.

@marcov, this is only an exercice about Generics writen in Delphi that I wanted to translate to Lazarus to try to aplicate this technique in order to solve a problem in an aplication. I'm not an expert in lazarus, so I'm sure that there will be better solutions to my problem, but that is not the case. What I really want to know is, like I've told before, why the code in Delphi mode works correctly and fails in FPC mode?

Anyway, thanks again to all for your interest

[marcov]

What I really want to know is, like I've told before, why the code in Delphi mode works correctly and fails in FPC mode?

Exactly because of what I said. That construct (with one identifier shadowing the other) is considered bad behaviour, and objfpc mode was meant as a cleaned up version of Delphi, so doesn't allow it.

[janasoft]

Many thanks @marcov. My doubt is solved.