On Sun, 4 Jun 2006 13:47:24 +0300
Al Boldi <[EMAIL PROTECTED]> wrote:
> Mattias Gaertner wrote:
> > Al Boldi <[EMAIL PROTECTED]> wrote:
> > > Flavio Etrusco wrote:
> > > > On 6/3/06, Al Boldi wrote:
> > > >> In the fpc-rtl there is something like this:
> > > >>
> > > >> procedure TObject.Free;
> > > >> begin
> > > >> if self<>nil then self.destroy;
> > > >> end;
> > > >>
> > > >> Does this make sense? i.e. How is it possible for self to be nil?
> > > >
> > > > 'Self' isn't a global variable associated with the method, it's
> > > > simply a parameter passed implicitly to the method.
> > >
> > > This would imply, that we are executing the class method instead of
> > > the object method.
> >
> > No. The 'Self' of a class method is the class.
> > The Self=nil test is useful for this case:
> >
> > var o: TObject;
> >
> > o:=TObject.Create;
> > ...
> > o.Free;
> > o:=nil;
> > ...
> > o.Free;
> >
> > The o is given to the method as hidden parameter, accessible via Self.
>
> Only the constructor should be possible to be called w/o self. All others
> should be dependent on a valid self, otherwise we get something like this:
>
> var obj: TObject;
>
> TObject.Free; // this won't compile, which is correct
> obj.Free; // this will compile, which is correct,
> // and gets warned of not being initialized,
> // but the error only gets detected inside
> // the class method, which is incorrect,
> // as it should have been detected in the
> // calling routine during execution.
>
> This problem gets really bad, when you have large class hierarchies, as
> the error may only be detected in some deep object without reference to
> the causing routine.
Yes, and no.
Yes, because it happens frequently. And no, it is not a big problem, because
the gdb backtrace shows it quite clear.
> Michael Van Canneyt wrote:
> > Al Boldi wrote:
> > > Does FPC have a switch to disallow executing class/definition methods,
> > > and only allow executing object/instance methods?
> >
> > No. What on earth would be the use of that ?
>
> This would make it easier to detect the causing routine of a
> non-initialized self.
I'm not sure, what you mean. It is calling the instance method, not a class
method.
Mattias
_________________________________________________________________
To unsubscribe: mail [EMAIL PROTECTED] with
"unsubscribe" as the Subject
archives at http://www.lazarus.freepascal.org/mailarchives
