how to create different class constructor and variable for it ?

[paule32]

Hello,
in my own Class System, I encounter a Problem with Constructors.
I using the Source Code as follows ...
Where is my mistake ?
I marked the Position, but I don't know how to fix it ...
So, a helping Hand is welcome ...

Code: Pascal  [Select][+][-]

1. type
2.   TClassForm = class of TForm;
3.   TApplication = class
4.   ...
5.   end;
6.   TForm = class
7.   ...
8.   end;
9.  
10. procedure TApplication_CreateForm(p: TApplication; InstanceClass: TFormClass; out Referenz ); stdcall;
11. begin
12.   TForm(Referenz) := TForm(InstanceClass).Create;   // <--- crash !!!
13. end;
14.  
15. procedure TApplication.CreateForm(InstanceClass: TFormClass; out Referenz); stdcall;
16. begin
17.   TApplication_CreateForm(self, InstanceClass, Referenz);
18. end;
19.  
20. type
21.   TForm1 = class(TForm1)
22.   ...
23.   end;
24. var
25.   Form1: TForm1;
26. begin
27.   Application := TApplication.Create;
28.   Application.CreateForm(TForm1, Form1);
29. end;

[ALLIGATOR]

https://gitlab.com/freepascal.org/lazarus/lazarus/-/blob/fd9ebbb202100aa9fbac3fb4f6bd2ad140890655/lcl/include/application.inc#L2274

[ALLIGATOR]

Try this:

Code: Diff  [Select][+][-]

1. - TForm(Referenz) := TForm(InstanceClass).Create;
2. + TForm(Referenz) := TForm(InstanceClass.Create);

[paule32]

Thanks Alligator ...

I used a backup 5 days ago ...
I don't get it all back, but the main sources are traced back and works , now.

Don't know what the Error in my Source was.

[Remy Lebeau]

You don't even need to type-cast the InstanceClass at all since its a class of TForm and its Create() will return a TForm pointer:

Code: Pascal  [Select][+][-]

1. TForm(Referenz) := InstanceClass.Create;

[paule32]

Thanks Remy for your Reply.

Now, I get a Error on the following Code Place:

Code: Pascal  [Select][+][-]

1. generic procedure TStream_LoadFromFile<T>   (p: specialize TStream<T>; const FileName: string); stdcall; external RTLDLL;

The Output is:

Code: Bash  [Select][+][-]

1. T:\a\>fpc.exe -dDLLIMPORT -dLANGDEU -dDLLDEBUG -n -B -Twin64 -FE. -Fu. -O3 test.pas
2. Stream.pas(144,115) Error: Compilation raised exception internally
3. Fatal: Compilation aborted
4. An unhandled exception occurred at $00000001000ECD52:
5. EAccessViolation: Access violation
6.   $00000001000ECD52
7.   $00000001000EDE28
8.   $00000001000EE5AB
9.   $00000001000AE31F
10.   $000000010012F0C5
11.   $000000010012E921
12.   $000000010012EB4C
13.   $000000010012E00A
14.   $000000010010B07B
15.   $00000001000F0689
16.   $00000001000F0771
17.   $000000010016ED78
18.   $0000000100171B1A
19.   $000000010017460E
20.   $0000000100174643
21.   $0000000100174643
22.   $0000000100174643
23.  
24. Error: C:\FPC\3.2.2\win64\fpc\bin\x86_64-win64\ppcx64.exe returned an error exitcode

[bytebites]

You have another topic about that issue.

[Remy Lebeau]

Now, I get a Error on the following Code Place:

Code: Pascal  [Select][+][-]

1. generic procedure TStream_LoadFromFile<T>   (p: specialize TStream<T>; const FileName: string); stdcall; external RTLDLL;

I'm pretty sure you can't export a Generic function from a DLL to begin with. So what are you trying to accomplish with this?

[cdbc]

Hi

So what are you trying to accomplish with this?

From what I understand, he's trying to put/stuff the entire RTL into a dll, in order to minimize application size amo.
Regards Benny

[paule32]

The Problem is not, to use Generic's in DLL or EXE ...

Like @Remy wrote: It is NOT possible to "export" Generic's.

The Problem is, that FPC DO NOT realize the Construct and end-up with FPC Kernel Faults like you can see in the Ouput Window that I posted there ...

In this case, I would expect a Error / Warning / Hint

[Thaddy]

In your case we expect a crash.
It is very simple if you have implemented it correctly.

Code: Pascal  [Select][+][-]

1. {$mode objfpc}
2. uses sysutils;
3. type
4.  
5.   TMyobject = class
6.   private
7.     FMyName:shortstring;
8.   public
9.     constructor Create;reintroduce;
10.     constructor create(const aName:shortstring);
11.     constructor create(const aName:shortstring;postscript:integer);
12.     property MyName:ShortString read FMyName;
13.   end;
14.  constructor TMyObject.Create;
15.  begin
16.    inherited create;
17.    FMyname := 'Name goes here';
18.  end;
19.  
20.  constructor TMyObject.Create(const aName:shortstring);
21.  begin
22.    inherited create;
23.    FMyname := aName;
24.  end;
25.  
26.  constructor TMyObject.create(const aName:shortstring;postscript:integer);
27.  begin
28.    inherited create;
29.    FMyname := aName + inttostr(postscript);
30.  end;
31.  
32. var a,b,c:TMyObject;
33. begin
34.   a:= TMyObject.Create;
35.   b:= TMyObject.Create('A new Name');
36.   c:= TMyObject.Create('A numbered new name:',100);
37.   writeln(a.MyName);writeln(b.MyName);writeln(c.MyName);
38.   c.Free;b.Free;a.Free;
39.   readln;
40. end.