FriendUtils.h

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#pragma once
 
#include <TChain.h>
#include <TFile.h>
#include <TFriendElement.h>
#include <TNotifyLink.h>
#include <TObjString.h>
 
namespace Darwin::Tools {
 
class ChainSlice : public TChain
{
    Long64_t fBegin; 
    Long64_t fEnd;   
 
    auto GetLast () const
    {
        return fEnd >= 0 ? std::min(fEnd, TChain::GetEntries())
                         : TChain::GetEntries();
    }
 
public:
    // Disable copies.
    ChainSlice (const ChainSlice&) = delete;
 
    ChainSlice (Long64_t begin = 0, Long64_t end = -1)
        : fBegin(begin)
        , fEnd(end)
    {
        // Force creation of the friends list. This controls friend handling in
        // TChain::LoadTree, *also for the friends of the loaded TTree*. I
        // consider this a bug in ROOT.
        fFriends = new TList();
    }
 
    ChainSlice (const char * name,
                Long64_t begin = 0,
                Long64_t end = -1,
                const char * title = "")
        : TChain(name, title)
        , fBegin(begin)
        , fEnd(end)
    {
        // Force creation of the friends list. This controls friend handling in
        // TChain::LoadTree, *also for the friends of the loaded TTree*. I
        // consider this a bug in ROOT.
        fFriends = new TList();
    }
 
    // Only to have something in the source file for linking purpose.
    virtual ~ChainSlice ();
 
    Long64_t GetBegin () const { return fBegin; }
 
    Long64_t GetEnd () const { return fEnd; }
 
    void SetBegin (Long64_t begin) { fBegin = begin; }
 
    void SetEnd (Long64_t end) { fEnd = end; }
 
    Long64_t GetEntries () const override { return GetLast() - GetBegin(); }
 
    Long64_t GetEntriesFast () const override { return GetEntries(); }
 
    Int_t GetEntry (Long64_t entry, Int_t getall = 0) override
    { return TChain::GetEntry(entry + GetBegin(), getall); }
 
    Long64_t GetReadEntry () const override { return TChain::GetReadEntry() - GetBegin(); }
 
    Long64_t GetReadEvent () const override { return GetReadEntry(); }
 
    Long64_t LoadTreeFriend (Long64_t entry, TTree * parent) override
    { return TChain::LoadTreeFriend(entry + GetBegin(), parent); }
 
    void Print (Option_t *) const override;
 
    ClassDefOverride(ChainSlice, 1)
};
 
class SlicedFriendElement : public TFriendElement
{
    Long64_t fBegin =  0; 
    Long64_t fEnd   = -1; 
 
    TList * fTrees = nullptr;
 
    ChainSlice * fChain = nullptr;            
    bool fOwnsChain = false;                  
    TNotifyLink<SlicedFriendElement> fNotify; 
 
public:
    SlicedFriendElement (): fNotify(this) {}
    SlicedFriendElement (TTree * parent,
                         ChainSlice * friendChain,
                         const char * alias);
    virtual ~SlicedFriendElement();
 
    static SlicedFriendElement * AddTo (TTree * tree,
                                        ChainSlice * chain,
                                        const char * alias);
 
    TTree * GetTree () override;
    TFile * GetFile () override;
 
    TList * GetListOfTrees () const { return fTrees; }
 
    Long64_t GetBegin () const { return fBegin; }
 
    Long64_t GetEnd () const { return fEnd; }
 
    bool Notify () override;
    void Print (Option_t * opt = 0) const override;
 
    ClassDefOverride(SlicedFriendElement, 1)
};
 
} // namespace Darwin::Tools