Re: [fpc-devel] Warning: Constructor should be public
2009/4/6 Flávio Etrusco : > Actually, your constructor has the same signature as 'TObject.Create', > so it should show a 'lower visibility' warning in Delphi, doesn't it? Correct, Delphi should also give this warning. > But, indeed, FPC shows the warning (should be public) for all > constructors, even if you're not hiding from the parent class, and I > always found this a (minor) annoyance. See my previous reply. Lowering visibility in descendant classes are breaking a contract (class interface) that was previously declared. Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://opensoft.homeip.net/fpgui/ ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Warning: Constructor should be public
On Mon, Apr 6, 2009 at 10:37 PM, Léo Willian Kölln wrote:
> No.
> See my singleton example:
How did I guess it was going to be about implementing a Singleton.
This issue has been raised a thousand times in FPC and Delphi circles.
:)
>
> TLoggerGeral = class
Which means you are descending from TObject.
> private
> {$IFDEF WINDOWS}
>class var FInstance : TLoggerGeral;
> {$ELSE}
>{$STATIC on}
>FInstance : TLoggerGeral; static;
> {$ENDIF}
>
>constructor Create;
Which means you are trying to lower the constructor TObject.Create
from public to private.
>
> A normal singleton and it complain!
I have a much easier "lazy man's" singleton for you... It's not 100%,
but then, I have *never* seen a singleton implementation in Delphi or
FPC that is 100%. Simply access the singleton via the gMySingleton
method.
eg:
gMySingleton.DoSomethingCool;
interface
TMySingleton = class(TObject)
...
end;
function gMySingleton: TMySingleton
implementation
var
uMySingleton: TMySingleton;
function gMySingleton: TMySingleton;
begin
if not Assigned(uMySingleton) then
uMySingleton := TMySingleton.Create;
result := uMySingleton;
end;
[...snip the rest of TMySingleton implementation...]
initialization
uMySingleton := nil;
finalization
uMySingleton.Free;
end.
The reason you can't lower the visibility of the constructor or any
method for that matter... A class interface (implementation section) ,
even for TObject as in your example, is a contract of how you can use
that class and what is available to you. By lowering the visibility
of a method or constructor in a descendant class, you are breaking the
contract previously defined. This is a BIG no-no, hence the reason it
is not allowed.
Regards,
- Graeme -
___
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http://opensoft.homeip.net/fpgui/
___
fpc-devel maillist - fpc-devel@lists.freepascal.org
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Re: [fpc-devel] Warning: Constructor should be public
Actually, your constructor has the same signature as 'TObject.Create',
so it should show a 'lower visibility' warning in Delphi, doesn't it?
But, indeed, FPC shows the warning (should be public) for all
constructors, even if you're not hiding from the parent class, and I
always found this a (minor) annoyance.
But the fact that the semantic of constructors in Delphi/ObjectPascal
have the same visibility rules of "common methods" (i.e. they force
the visibility of the constructor from the parent class) is just sad.
"Even" Java constructors' syntax is better ;-)
Not to mention that you can call constructors on instance "pointer"
(ok, I know this "hack is useful/used in streaming/persistence code),
even uninitialized ones...
-Flávio
On Mon, Apr 6, 2009 at 5:37 PM, Léo Willian Kölln wrote:
> No.
> See my singleton example:
>
> TLoggerGeral = class
> private
> {$IFDEF WINDOWS}
> class var FInstance : TLoggerGeral;
> {$ELSE}
> {$STATIC on}
> FInstance : TLoggerGeral; static;
> {$ENDIF}
>
> constructor Create;
>
> protected
> pCritSection : TCriticalSection;
> pLogarDatas : boolean;
> pLogarTipos : boolean;
> pArquivoDestino : TextFile;
> saidaConsole : boolean;
>
> class function getData: String;
> class function tipoText(tipo: ETipoMensagem): String;
> class procedure executaOperacaoPrioridade(tipo: ETipoMensagem);
>
> public
> destructor Destroy; override;
> class function GetInstance: TLoggerGeral;
> class procedure recebeMensagem(const mensagem: String; tipo:
> ETipoMensagem = NORMAL);
> end;
>
> A normal singleton and it complain!
>
> Léo Willian Kölln
>
>
> On Mon, Apr 6, 2009 at 4:41 PM, Graeme Geldenhuys
> wrote:
>>> Simply question. Why?
>>
>>
>> What did you do, try and lower the visibility of the constructor? If
>> so, that is also not allowed in Delphi as far as I know.
>>
>> Regards,
>> - Graeme -
>>
>>
>> ___
>> fpGUI - a cross-platform Free Pascal GUI toolkit
>> http://opensoft.homeip.net/fpgui/
>> ___
>> fpc-devel maillist - fpc-de...@lists.freepascal.org
>> http://lists.freepascal.org/mailman/listinfo/fpc-devel
>>
> ___
> fpc-devel maillist - fpc-de...@lists.freepascal.org
> http://lists.freepascal.org/mailman/listinfo/fpc-devel
>
___
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Re: [fpc-devel] Warning: Constructor should be public
No.
See my singleton example:
TLoggerGeral = class
private
{$IFDEF WINDOWS}
class var FInstance : TLoggerGeral;
{$ELSE}
{$STATIC on}
FInstance : TLoggerGeral; static;
{$ENDIF}
constructor Create;
protected
pCritSection: TCriticalSection;
pLogarDatas : boolean;
pLogarTipos : boolean;
pArquivoDestino : TextFile;
saidaConsole: boolean;
class function getData: String;
class function tipoText(tipo: ETipoMensagem): String;
class procedure executaOperacaoPrioridade(tipo: ETipoMensagem);
public
destructor Destroy; override;
class function GetInstance: TLoggerGeral;
class procedure recebeMensagem(const mensagem: String; tipo:
ETipoMensagem = NORMAL);
end;
A normal singleton and it complain!
Léo Willian Kölln
On Mon, Apr 6, 2009 at 4:41 PM, Graeme Geldenhuys
wrote:
>> Simply question. Why?
>
>
> What did you do, try and lower the visibility of the constructor? If
> so, that is also not allowed in Delphi as far as I know.
>
> Regards,
> - Graeme -
>
>
> ___
> fpGUI - a cross-platform Free Pascal GUI toolkit
> http://opensoft.homeip.net/fpgui/
> ___
> fpc-devel maillist - fpc-de...@lists.freepascal.org
> http://lists.freepascal.org/mailman/listinfo/fpc-devel
>
___
fpc-devel maillist - fpc-devel@lists.freepascal.org
http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Warning: Constructor should be public
> Simply question. Why? What did you do, try and lower the visibility of the constructor? If so, that is also not allowed in Delphi as far as I know. Regards, - Graeme - ___ fpGUI - a cross-platform Free Pascal GUI toolkit http://opensoft.homeip.net/fpgui/ ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
[fpc-devel] Warning: Constructor should be public
Simply question. Why? In Delphi i don´t need this, and on ObjPascal i don´t see why this is necessary... This warning happens even when i use the Delphi compatibility mode! Léo Willian Kölln ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
