Mattias Gaertner wrote:
> 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.
You wish. obj.Free calls the class method regardless of self's validity.
Calling the instance method could ensure a valid self always.
Thanks!
--
Al
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