[fpc-pascal] TObject

[Joao Morais]

Carsten Bager wrote:
> A have a unit (uSafeVar) with an object. The object has a property "data" of the type 
> "SafeVar_typ"
> 
> If I do this it works (wSafeVar is called)
> 
> var
>   p:SafeVar_typ;
> begin
>   p.d:=111;
>   SafeVar.data:=p;

Here the Data setter is called, ie, wSafeVar, because you are assigning 
a new value to it.

> end
> 
> 
> If I do this it dos not work but it compiles (wSafeVar is not called)
> 
> begin
>   SafeVar.data.d:=111;

Here the Data getter is called, ie, hSafeVar, because you are reading a 
value from it.

Use a function as a getter instead of a class member. Btw getters and 
setters have not the same syntax, you need to create two different methods.

--
Joao Morais


> end;
> 
> If I do a read like this ( after the line SafeVar.data.d:=111;)
> Writeln(SafeVar.data.d);
> the output is 111
> 
> The compiler is
> Free Pascal Compiler version 2.2.2 [2008/08/26] for arm
> 
> Of course I could create a property fore every variable I want to save, but in the real 
> program it is a big record, so I thought this was a smart way to get around this.
> Is it in fact an error that it compiles?
> 
> 
> Carsten
> 
> 
> --------------------------------------------------------------------------
> Unit uSafeVar;
> {$mode objfpc}
> 
> 
> Interface
> 
> Uses
>   sysutils,
>   Classes;
> 
> Type
>   SafeVar_typ = packed record
>       d:byte;
>   end;
> 
>   TSafeVar=class(TObject)
>     Private
>       hSafeVar:SafeVar_typ;
>       f:file of SafeVar_typ;
>       Procedure wSafeVar(data:SafeVar_typ);
>     Public
>       constructor create;
>       destructor destroy; override;
>       property data:SafeVar_typ read hSafeVar write wSafeVar;
>     Published
>   end;
> 
> 
> 
> var
>   SafeVar:TSafeVar;
> 
> implementation
> 
> constructor TSafeVar.create;
> Begin
>   inherited Create;
>   fillchar(hSafeVar,sizeof(SafeVar_typ),chr(0));
>   assign(f,SafeVar_dat);
>   if fileexists(SafeVar_dat) then
>   begin
>     reset(f);
>     read(f,hSafeVar);
>   end else
>   begin
>     rewrite(f);
>     Write(f,hSafeVar);
>   end;
> End;
> 
> destructor TSafeVar.destroy;
> Begin
>   inherited destroy;
>   close(f);
> End;
> 
> Procedure TSafeVar.wSafeVar(data:SafeVar_typ);
> Begin
>   hSafeVar:=data;
>   seek(f,0);
>   Write(f,data);
> End;
> 
> initialization
>   SafeVar:=tSafeVar.create;
> finalization
>   SafeVar.free;
> End.
> ------------------------------------------
>