[TTreeReader] Unable to read TBranchObject

Problems with RDataFrame and TBranchObjects first reported on the forum here.

Using the file provided by the forum user, at https://cernbox.cern.ch/index.php/s/CcgXcCJMweaaTck , a simple reproducer for the issue is:

#include <TFile.h>

#include <TTreeReader.h>

#include <TTreeReaderValue.h>

#include <TH2F.h>

int main()

{

        TFile *_file0 = TFile::Open("dqmio.root");

        TTree *MEs = nullptr;

        _file0->GetObject("MEs", MEs);

        TTreeReader r(MEs);

        TTreeReaderValue<TH2F> histo(r, "value");

        r.Next();

        *histo;

        return 0;

}

which prints Error in <TBranchProxy::Read>: Unable to initialize value.

The problem seems to be that TBranchProxy::Setup does not have any logic to deal with TBranchObject s, cannot retrieve the value address (fWhere ) and therefore returns false at TBranchProxy.cxx:487 .