Hi Christian,
TFolders are not a replacement for normal C++ pointers.
In a C++ program, I will consider the following cases:
-A: very strong coupling. You put together all items
that have to be used together. This is the class level.
-B: A logical structures (a tree/graph) of classes that must
always be used together.
-C: A large network of classes
In a large system, you can imagine all possible combinations
- everything in one single class ::)
- the other extreme: too many classes
- the most usual case: something between the two extreme cases
When the system grows, it is important to minimize class dependencies
for many reasons:
- a practical reason. If you make a change to one class, you do not
want to recompile too many classes.
- you want to structure your super large system into sub systems
that could be used independently or maintained independently.
- you want to minimize the side effects of a change in some class
design.
Your particular example is clearly in category B above. You will
still benefit in posting your Tlist objects in some folder. This has the
big advantage that you have a standard way to navigate/browse in your
class network. This is important in large collaborations and it helps
in documentating a system.
The big advantage of TFolders come only when the system grows.
The main objects like Collections, Geometry, MagFields can be reached
via the TFolder naming scheme instead of getting a pointer to some class
that you know holds in turn a pointer to one of these objects.
My message is the following: Do not abuse of TFolder as a replacement
for something that is better implemented by a class or standard
collections.
When your system grows, minimize the coupling by obtaining your pointers
from the naming scheme ("a/b/c/..") of folders instead of getting a
pointer from some super manager class.
Rene Brun
On Wed, 24 Oct 2001, cstrato@EUnet.at wrote:
> Dear Rene
>
> Thank you for your reply. At the moment I am just testing different
> approaches to see what I could use.
>
> Probably, I do not quite understand the concept of TFolder helping
> to minimize the coupling between classes. Suppose, I have the
> following classes:
>
> ClassA
> TList fListClassA //list of ClassA!
> TList fListClassB
>
> ClassB
> TList fListClassA
> TList fListClassC
>
> ClassC
> TList fListClassB
>
> How can TFolder help me to minimize the coupling between these
> classes?
>
> Thank you in advance
> Christian
>
>
> Rene Brun wrote:
>
> > Hi Christian,
> >
> > The primary role of TFolder is to facilitate the description of the
> > transient data structures, minimizing strong coupling between classes.
> > Your folder structure is correct. However, your structure mimics a Unix
> > directory structure. It is not what a TFolder is designed for.
> > Why don't you use directly the OS file system to do this?
> >
> > Anyhow, assuming your existing folder structure, you can automatically
> > generate a Root Tree from this structure by doing for example:
> >
> > TFile *vFile = new TFile("folders.root","recreate");
> > TTree T("T","/MyRoot");
> > T.Fill();
> > T.Print();
> > T.Write();
> >
> > instead of the last 3 statements of your function MyFolders.
> > The T.Print() will show you the automatic generation of the Tree branches
> > from the folder structure. There is no need to specify branch addresses.
> >
> > Currently, Root is not capable of rebuilding the folder structure automatically
> > when reading back a Tree. This is on my todo list since a few months now.
> >
> > Rene Brun
> >
> >
> > > ----------------------------------
> > > C.h.r.i.s.t.i.a.n S.t.r.a.t.o.w.a
> > > V.i.e.n.n.a, A.u.s.t.r.i.a
> > >
>
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