objfpc and delphi mode callbacks
lazarus / 62-General

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Zaher · 2018-04-02 17:28

I got error Wrong number of parameters  when i pass callback function
in objfpc, and the function declared other unit in delphi mode

Error: Wrong number of parameters specified for call to "MyCallback2"
Error: Found declaration: MyCallback2(AnsiString);

Unit2
Code: [Select]unit Unit2;

{$mode delphi}{$H+}

interface

uses
  Classes, SysUtils;

type
  TMyCallback = procedure(S: string);

procedure CallIt(const ACallback: TMyCallback);

implementation

procedure MyCallback1(S: string);
begin
end;

procedure CallIt(const ACallback: TMyCallback);
begin
  ACallback('Hello');
end;

end.



Here where i call it

Code: [Select]procedure MyCallback2(S: string);
begin
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  CallIt(MyCallback2);
end;

I need to use CallIt and pass mycallback2 without using @ pointer of
procedure, i don't to lose checking parameters benefits , or using
delphi mode in unit1.

is there any way to solve it?

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molly · 2018-04-02 17:54

Quote from: Zaher on April 02, 2018, 07:28:23 pmI need to use CallIt
and pass mycallback2 without using @ pointer of procedure, i don't to
lose checking parameters benefits , or using delphi mode in unit1.

is there any way to solve it?
Code: [Select]{$modeswitch CLASSICPROCVARS}
?

More info.

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Zaher · 2018-04-02 18:16

Yes that help, but still need to understand why there is different?
Maybe I can change the parameters to suite with callback proc

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rvk · 2018-04-02 18:25

Quote from: Zaher on April 02, 2018, 07:28:23 pmI need to use CallIt
and pass mycallback2 without using @ pointer of procedure, i don't to
lose checking parameters benefits , or using delphi mode in unit1.
I'm not sure I understand... but what's the problem with using @ in
this case in unit1?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+}//...procedure TForm1.FormCreate(Sender:
TObject);begin  CallIt(@MyCallback2);end;
A.F.A.I.K. you don't "lose checking parameters benefits" when passing
it with @, or am I missing something?

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Zaher · 2018-04-02 18:29

The problem if I changed the parameters of TMyCallback, I need the
compiler stops me, to correct my functions
With passing pointer, compiler work, but at runing time, I got AV.

Code: [Select]type
  TMyCallback = procedure(S: string; ID: Integer);

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rvk · 2018-04-02 18:31

Ah, ok. How about using {$typedaddress on} in unit2?

QuoteAlso, if you are using the @-address-operator usage of
{$typedaddress on} is advised in order to prevent programming
mistakes.http://wiki.freepascal.org/How_to_use_procedural_variables

B.T.W. I still got an "Incompatible type for arg no. 1" error even
without it.

Code below gives me:
Quoteunit1.pas(39,22) Error: Incompatible type for arg no. 1: Got
"<address of procedure(AnsiString);Register>", expected "<procedure
variable type of procedure(AnsiString;LongInt);Register>"Which seems
fine.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, Forms,
Controls, Graphics, Dialogs, StdCtrls; type   { TForm1 }   TForm1 =
class(TForm)    Button1: TButton;    procedure FormCreate(Sender:
TObject);  private   public   end; var  Form1:
TForm1; implementationuses Unit2; {$R *.lfm} { TForm1 }procedure
MyCallback2(S: string);begin  Showmessage(S);end; procedure
TForm1.FormCreate(Sender: TObject);begin 
CallIt(@MyCallback2);end; end.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit2; {$mode delphi}{$H+} interface uses  Classes, SysUtils; type 
TMyCallback = procedure(S: string; ID: Integer); procedure
CallIt(const ACallback: TMyCallback); implementation procedure
CallIt(const ACallback: TMyCallback);begin  ACallback('Hello',
2);end; end.

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Zaher · 2018-04-02 18:52

Oh, my fault,

Yes when i used @ the compiler still check the params, in objfpc,

It is my fault, but i am sure I tested it before posting here O.o