[fpc-pascal] Could someone explain me which the correct triggering of the BeforeDestruction method?

[Luiz Americo Pereira Camara]

Seems that Delphi considers that the object is already created at the time
AfterConstruction is called, so it understands that when it gets into
AfterConstruction is sucessfully created. Semantically makes sense.

The counter proof is see if AfterConstruction is called when a exception
occurs in constructor

Luiz

Em 3 de set de 2016 11:50 PM, "silvioprog" <silvioprog at gmail.com> escreveu:

> Hello,
>
> My question at title seems stupid, but the reason why I've get this doubt
> is just because it get different results between Free Pascal and Delphi in
> the following example:
>
> === begin code ===
>
> program project1;
>
> {$IFDEF FPC}
>   {$MODE DELPHI}
> {$ENDIF}
> {$IFDEF MSWINDOWS}
>   {$APPTYPE CONSOLE}
> {$ENDIF}
>
> uses SysUtils;
>
> type
>   TSomeClass = class
>   public
>     procedure LoadSomething;
>   end;
>
>   TA = class
>   private
>     FSomeObject: TSomeClass;
>   public
>     constructor Create; virtual;
>     destructor Destroy; override;
>     procedure AfterConstruction; override;
>     procedure BeforeDestruction; override;
>     property SomeObject: TSomeClass read FSomeObject;
>   end;
>
> procedure TSomeClass.LoadSomething;
> begin
>   raise Exception.Create('An exception loading something');
> end;
>
> constructor TA.Create;
> begin
>   WriteLn(1);
>   inherited Create;
> end;
>
> destructor TA.Destroy;
> begin
>   WriteLn(2);
>   inherited Destroy;
> end;
>
> procedure TA.AfterConstruction;
> begin
>   WriteLn(3);
>   FSomeObject := TSomeClass.Create;
>   FSomeObject.LoadSomething;
> end;
>
> procedure TA.BeforeDestruction;
> begin
>   WriteLn(4);
>   FSomeObject.Free;
> end;
>
> var
>   VA: TA;
> begin
>   VA := TA.Create;
>   try
>   finally
>     VA.Free;
>   end;
> end.
>
> === end code ===
>
> I've compiled it in Free Pascal from trunk (version 3.1.1 [2016/08/26] for
> x86_64) installed on a Xubuntu 16.04 64 bits, and got the following log:
>
> $ ./project1
> 1
> 3
> 2
> An unhandled exception occurred at $00000000004001CD:
> Exception: An exception loading something
>   $00000000004001CD  LOADSOMETHING,  line 30 of project1.lpr
>   $000000000040045A  AFTERCONSTRUCTION,  line 50 of project1.lpr
>   $00000000004002CC  CREATE,  line 38 of project1.lpr
>   $00000000004004FA  main,  line 62 of project1.lpr
>
> and I've compiled the same code in an original version of Delphi Pro
> (version 10.1 Berlin 24.0.22858.6822), on a Windows 10 64 bits, and I got
> the log below and a critical exception (notice the result numbers, they are
> different from similar test compiled in Free Pascal):
>
> Win32\Debug>Project1.exe
> 1
> 3
> 4
> 2
> ^C
>
> (I need to kill the app by Ctrl+C within terminal)
>
> the critical exception was the known:
>
> [Main Instruction]
> Project1.exe has stopped working
>
> [Content]
> Windows is checking for a solution to the problem...
>
> So, is it a bug? If so, in which compiler?! Even after reading some
> documents about BeforeDestruction I still have doubt about which is the
> correct triggering of this method, and I would be glad if someone could
> help me to solve it.
>
> --
> Silvio Clécio
>
> _______________________________________________
> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
>
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