ROOT containers: do they need to know about gROOT ?

Pasha Murat (murat@cdfsga.fnal.gov)
Mon, 16 Mar 1998 17:38:11 -0600 (CST)

Hello,
there is one issue which could be of interest for general discussion.
ROOT has a pretty nice set of collection classes and I've been asked several
times whether it is possible to use them outside the context of ROOT (means
without TROOT object being initialized in the code.)

Trying to find an answer I realized that some of the container
classes (like TObjArray) could be used outside ROOT, others (like TOrdCollection)
require TROOT object to be initialized.

The thing which confuses me a little bit is the following.
TOrdCollection class uses RTTI when TOrdCollection::IndexOf(TObject *obj)
tries to define location of the object in the list. Here is its source
code (taken from 1.03/09):
--------------------------------------------------------------------------------
Int_t TOrdCollection::IndexOf(TObject *obj) const
{
// Return index of object in collection. Returns -1 when object not found.
// Uses member IsEqual() to find object.

for (Int_t i = 0; i < GetSize(); i++)
if (fCont[PhysIndex(i)]->IsEqual(obj))
return i;

return -1;
}
--------------------------------------------------------------------------------
TOrdCollection::IsEqual calls ROOT RTTI.

Given the collection contains pointers to TObjects, why is it necessary to
use RTTI when comparing TObject* to TObject* ? Isn't it enough just to compare
to pointers to each other? Or this is related to ROOT I/O and persistency
mechanism?

Thanks, Pasha.