> "Why does the def constr have to be public?"
Default constructor is inevitable for reading class from file.
CINT generates some code to create the class by class name.
> "For the time being: Is there a workaround?"
There is no workaround. It is limitation, but I think,
very small limitation.
Victor
George Irwin wrote:
>
> Hi Rene, Apart from the issue of a special constructor with
> TBuffer argument, I'm curious about the answers to Axel's other
> questions:
>
> "Why does the def constr have to be public?"
>
> "For the time being: Is there a workaround?"
>
> Thanks. George
>
> > Hi Axel,
> > There are several cases where Root has to create an object.
> > - creation of a branch with an object
> > - Input when Streaming in TBuffer::ReadObject
> > - Object Inspection
>
> > - Creation of a context menu
> > - html code generator
> >
>
> > We try to eliminate as much as possible the calls to the default
> constructor
> > in the case of TTrees. But it would not be wise to have a special
> constructor
> > with a TBuffer argument, another one for inspection, etc.
> > In all the above cases, Root has to build a class dictionary to
> store
> > the member types and offsets in the class. This is done by calling
> > the object::ShowMembers function provided by the ClassDef macro.
> >
>
> > Rene Brun
> >
>
> > Axel Naumann wrote:
> > >
>
> > > Hi,
> > >
>
> > > I have the following problem: I want to protect a class's default
> > > constructor from the outside world (declare it as private, as no
> object of
> > > this type may be allocated). Even adding TClass as friend does
> not help (is
> > > that a rootcint parsing limitation or is the ::new actually
> called in some
> > > other class?).
> > >
>
> > > Of course I would prefer a more general approach. One could ask:
> Why does
> > > the def constr has to be public? Actually the object is
> initialized by the
> > > Streamer's TBuffer. So in principle there should be a public:
> > > TMyObj::TMyObj(TBuffer&), which only calls the object's (e.g.
> private) def
> > > constr. It might look like an unnecessary overhead, but I think
> it makes
> > > sense: If you have a buffer to initialize my members you may use
> my
> > > constructor, otherwise: hands off. One could even add this constr
> to the
> > > ClassDef macro:
> > >
>
> > > public: inline name::name(TBuffer&): name::name(){};
> > >
>
> > > so the user would get a linker error not implementing the def
> const. I know
> > > this is not the "usual" implementation of streamers, most
> streamers
> > > explicitely require a public def constr. But I find this handier
> and
> > > cleaner. I don't really know what this would mean in terms of
> backwards
> > > compatibility, but it looks fine to me at first sight.
> > >
>
> > > For the time being: Is there a workaround?
> > >
>
> > > Best regards, Axel
--
Victor M. Perevoztchikov perev@bnl.gov perev@vxcern.cern.ch
Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000
tel office : 631-344-7894; fax 631-344-4206; home 631-345-2690
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