Generic type nil problem
lazarus / 62-General

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J-23 · 2020-09-29 22:39

Hello,
I wanted to present some code that shows some inconsistency in
specifying type in generic classes.

Maybe it is worth considering improving this in the next FPC versions,
but before I can report it, I wanted to know the opinions, hence the
publication on the forum.

Having the code:
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 type   {
TBaseWizardDialogEditorClass }   generic
TBaseWizardDialogEditorClass<T; F: TBaseWizardForm> = class(TObject) 
private    FOnActionClose: TCloseEvent;    FOnMasterDataSetField:
TOnMasterDataSetField;    procedure SetOnActionClose(AValue:
TCloseEvent);    procedure SetOnMasterDataSetField(AValue:
TOnMasterDataSetField);  protected    FFormWizard: F;    procedure
DoActionButton(Sender: TObject); virtual; abstract;    procedure
EditObject(EditObject: T); virtual; abstract;  public    destructor
Destroy; override;    procedure Show; virtual;    procedure Clear;
virtual; abstract;    procedure DefaultValueComponent; virtual;
abstract;    procedure DefaultValueComponent(DataSetValue: string);
virtual; abstract;    property OnActionClose: TCloseEvent read
FOnActionClose write SetOnActionClose;    property
OnMasterDataSetField: TOnMasterDataSetField read FOnMasterDataSetField
write SetOnMasterDataSetField;  end; implementation  {
TBaseEditorClass } procedure TBaseEditorClass.DoActionClose(Sender:
TObject;  var CloseAction: TCloseAction);begin  FActionTypeEditor :=
ateAdd;end; procedure TBaseEditorClass.Edit(Item: T);begin 
FActionTypeEditor := ateEdit;end; procedure
TBaseEditorClass.Show;begin  case FActionTypeEditor of    ateAdd:
FWizardEditor.Show;    ateEdit: FWizardEditEditor.Show;  end;end; {
TBaseWizardDialogEditorClass } procedure
TBaseWizardDialogEditorClass.SetOnActionClose(AValue:
TCloseEvent);begin  if FOnActionClose = AValue then Exit; 
FOnActionClose := AValue;end; procedure
TBaseWizardDialogEditorClass.SetOnMasterDataSetField(  AValue:
TOnMasterDataSetField);begin  if FOnMasterDataSetField = AValue then
Exit;  FOnMasterDataSetField := AValue;end; destructor
TBaseWizardDialogEditorClass.Destroy;begin  if FFormWizard <> nil
then    FreeAndNil(FFormWizard);  inherited Destroy;end; procedure
TBaseWizardDialogEditorClass.Show;begin 
FFormWizard.ShowModal;end; end.
Due to the fact that in line 65 there is:

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 if
FFormWizard <> nil then
I get the message (during compilation):
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
WizardDialogEditorRBM.pas(119,21) Error: Incompatible types: got
"Pointer" expected "$gendef1"
Which clearly indicates that I do not know if type is a pointer, hence
the above message and it would be true if I declared my class like
this:

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  generic
TBaseWizardDialogEditorClass<T; F> = class(TObject)
but my class declaration specifies the type so the above message
shouldn't be. (According to me)

What do you think about it? Is it worth reporting it?


A few words on this topic
https://forum.lazarus.freepascal.org/index.php?topic=42009.0 were
mentioned in this thread that it is like Delphi is similar but I do
not have how to check it now.


Even if it were, there would be no consequences for a notation like
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 <T; F:
TBaseWizardForm>

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Blaazen · 2020-09-29 23:01

I tried your code with 3.3.1 - yesterday trunk, {$mode objfpc} and I
got no error message for both variants, i.e. both:
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 generic
TBaseWizardDialogEditorClass<T; F: TBaseWizardForm> =
class(TObject)andgeneric TBaseWizardDialogEditorClass<T; F> =
class(TObject)compiles well.

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J-23 · 2020-09-29 23:13

Quote from: Blaazen on September 30, 2020, 01:01:50 amI tried your
code with 3.3.1 - yesterday trunk, {$mode objfpc} and I got no error
message for both variants, i.e. both:
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 generic
TBaseWizardDialogEditorClass<T; F: TBaseWizardForm> =
class(TObject)andgeneric TBaseWizardDialogEditorClass<T; F> =
class(TObject)compiles well.

Thanks for the information. I will try

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PascalDragon · 2020-09-30 08:16

Quote from: Blaazen on September 30, 2020, 01:01:50 amI tried your
code with 3.3.1 - yesterday trunk, {$mode objfpc} and I got no error
message for both variants, i.e. both:
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 generic
TBaseWizardDialogEditorClass<T; F: TBaseWizardForm> =
class(TObject)andgeneric TBaseWizardDialogEditorClass<T; F> =
class(TObject)compiles well.

Seems like I'll have to hunt for the revision that fixed that and have
that merged to 3.2.1...

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J-23 · 2020-09-30 10:53

I confirm it works.

However, there is a new problem with FPC 3.3.1 not compiling
FastReport when compiling I am getting a message:
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
frxXML.pas(475,22) Error: Asm: signed dword value exceeds bounds
-4294967296
It concerns the procedure:
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 procedure
TfrxXMLItem.SetOffset(const Value: Int64);begin  FHiOffset := Value
div $100000000;  FLoOffset := Value mod $100000000; //this errorend; 
Which will be in the file:
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 C:\Program
Files (x86)\FastReport 5 VCL Professional\Source\frxXML.pas
This problem was not present in the previous FPC version, but there
was a problem with the generics

I will only add that around the Lazarus 2.0.8 version, the generic
code that I presented earlier, Lazarus compiled it

How do I get around the problem so that I can install FastReport?

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PascalDragon · 2020-09-30 11:36

Quote from: J-23 on September 30, 2020, 12:53:21 pmHowever, there is a
new problem with FPC 3.3.1 not compiling FastReport when compiling I
am getting a message:
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
frxXML.pas(475,22) Error: Asm: signed dword value exceeds bounds
-4294967296
Are you compiling with -al or any -Axxx option? Cause that message
comes from the external assembler (though I can not reproduce it with
the as I have, at least not with a simple example code).

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J-23 · 2020-09-30 11:51

No, it compiles on standard options.

What information do you need to diagnose the problem?

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PascalDragon · 2020-09-30 20:26

As a first step your complete compiler commandline. Cause the error
message is from the external assembler as it does not exist in the
compiler.

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J-23 · 2020-10-01 00:28

Quote from: PascalDragon on September 30, 2020, 10:26:35 pmAs a first
step your complete compiler commandline. Cause the error message is
from the external assembler as it does not exist in the compiler.
OK, I'll check and give it, or even prepare a virtual machine that
shows the problem.

I will add that the problem only occurs on 64 bits on 32 bits,
everything is ok.