TEmulatedCollectionProxy.cxx

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// @(#)root/io:$Id$
// Author: Markus Frank 28/10/04
 
/*************************************************************************
 * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
 
/**
 \class TEmulatedCollectionProxy
 \ingroup io_other
 
Streamer around an arbitrary STL like container, which implements basic
container functionality.
 
### Note:
Although this class contains all the setup necessary to deal
with maps, the map-like functionality is NOT supported.
For optimization reasons this functionality is put into
the class TEmulatedMapProxy.
*/
 
#include "TEmulatedCollectionProxy.h"
#include "TStreamerElement.h"
#include "TStreamerInfo.h"
#include "TClassEdit.h"
#include "TError.h"
#include "TEnum.h"
#include "TROOT.h"
#include <iostream>
 
#include "TVirtualMutex.h" // For R__LOCKGUARD
#include "TInterpreter.h"  // For gInterpreterMutex
 
//
// Utility function to allow the creation of a TClass for a std::pair without
// a dictionary (See end of file for implementation
//
 
TEmulatedCollectionProxy::TEmulatedCollectionProxy(const TEmulatedCollectionProxy& copy)
   : TGenCollectionProxy(copy)
{
   // Build a Streamer for an emulated vector whose type is 'name'.
   fProperties |= kIsEmulated;
}
 
TEmulatedCollectionProxy::TEmulatedCollectionProxy(const char *cl_name, Bool_t silent)
   : TGenCollectionProxy(typeid(Cont_t), sizeof(Cont_t::iterator))
{
   // Build a Streamer for a collection whose type is described by 'collectionClass'.
 
   fName = cl_name;
   if ( this->TEmulatedCollectionProxy::InitializeEx(silent) ) {
      fCreateEnv = TGenCollectionProxy::Env_t::Create;
   }
   fProperties |= kIsEmulated;
}
 
TEmulatedCollectionProxy::~TEmulatedCollectionProxy()
{
   // Standard destructor
   if ( fEnv && fEnv->fObject ) {
      Clear();
   }
}
 
TVirtualCollectionProxy* TEmulatedCollectionProxy::Generate() const
{
   // Virtual copy constructor
 
   if ( !fClass ) Initialize(kFALSE);
   return new TEmulatedCollectionProxy(*this);
}
 
void TEmulatedCollectionProxy::Destructor(void* p, Bool_t dtorOnly) const
{
   // Virtual destructor
 
   if (!p) return;
   if (!fEnv || fEnv->fObject != p) { // Envoid the cost of TPushPop if we don't need it
      // FIXME: This is not thread safe.
      TVirtualCollectionProxy::TPushPop env(const_cast<TEmulatedCollectionProxy*>(this), p);
      const_cast<TEmulatedCollectionProxy*>(this)->Clear("force");
   } else {
      const_cast<TEmulatedCollectionProxy*>(this)->Clear("force");
   }
   if (dtorOnly) {
      WithCont(p, [](auto *c, std::size_t) {
         using Vec_t = std::decay_t<decltype(*c)>;
         c->~Vec_t();
      });
   } else {
      WithCont(p, [](auto *c, std::size_t) { delete c; });
   }
}
 
void TEmulatedCollectionProxy::DeleteArray(void* p, Bool_t dtorOnly) const
{
   // Virtual array destructor
 
   // Cannot implement this properly, we do not know
   // how many elements are in the array.
   Warning("DeleteArray", "Cannot properly delete emulated array of %s at %p, I don't know how many elements it has!", fClass->GetName(), p);
   if (!dtorOnly) {
      ::operator delete(p);
   }
}
 
TGenCollectionProxy *TEmulatedCollectionProxy::InitializeEx(Bool_t silent)
{
   // Proxy initializer
   R__LOCKGUARD(gInterpreterMutex);
   if (fClass) return this;
 
 
   TClass *cl = TClass::GetClass(fName.c_str(), kTRUE, silent);
   fEnv = 0;
   fKey = 0;
   if ( cl )  {
      int nested = 0;
      std::vector<std::string> inside;
      fPointers  = false;
      int num = TClassEdit::GetSplit(fName.c_str(),inside,nested);
      if ( num > 1 )  {
         std::string nam;
         if ( inside[0].find("stdext::hash_") != std::string::npos ) {
            inside[0].replace(3,10,"::");
         }
         if ( inside[0].find("__gnu_cxx::hash_") != std::string::npos ) {
            inside[0].replace(0,16,"std::");
         }
         fSTL_type = TClassEdit::STLKind(inside[0]);
         // Note: an emulated collection proxy is never really associative
         // since under-neath is actually an array.
 
         auto alignedSize = [](size_t in, TClass *align_cl) {
            size_t align = align_cl ? align_cl->GetClassAlignment() : alignof(std::max_align_t);
            return in + (align - in % align) % align;
         };
         struct GenerateTemporaryTEnum {
            TEnum *fTemporaryTEnum = nullptr;
 
            GenerateTemporaryTEnum(UInt_t typecase, const std::string &enumname)
            {
               if (typecase == kIsEnum && !TEnum::GetEnum(enumname.c_str())) {
                  fTemporaryTEnum = new TEnum();
                  fTemporaryTEnum->SetName(enumname.c_str());
                  gROOT->GetListOfEnums()->Add(fTemporaryTEnum);
               }
            }
 
            ~GenerateTemporaryTEnum()
            {
               if (fTemporaryTEnum) {
                  gROOT->GetListOfEnums()->Remove(fTemporaryTEnum);
                  delete fTemporaryTEnum;
               }
            }
         };
         switch ( fSTL_type )  {
            case ROOT::kSTLmap:
            case ROOT::kSTLmultimap:
               nam = "pair<"+inside[1]+","+inside[2];
               nam += (nam[nam.length()-1]=='>') ? " >" : ">";
               fKey   = new Value(inside[1],silent);
               fVal   = new Value(inside[2],silent);
               {
                  // We have the case of an on-file enum or an unknown class, since
                  // this comes from a file, we also know that the type was valid but
                  // since we have no information it was either
                  //   a. an enum
                  //   b. a class of type that was never stored
                  //   c. a class with a custom streamer
                  // We can "safely" pretend that it is an enum in all 3 case because
                  //   a. obviously
                  //   b. it will not be used anyway (no object of that type on the file)
                  //   c. since we don't know the class we don't have the Streamer and thus can read it anyway
                  // So let's temporarily pretend it is an enum.
                  GenerateTemporaryTEnum keyEnum(fKey->fCase, inside[1]);
                  GenerateTemporaryTEnum valueEnum(fVal->fCase, inside[2]);
 
                  if (0==TClass::GetClass(nam.c_str(), kTRUE, silent)) {
                     // We need to emulate the pair
                     TVirtualStreamerInfo::Factory()->GenerateInfoForPair(inside[1],inside[2], silent, 0, 0);
                  }
               }
               fValue = new Value(nam,silent);
               if ( !(*fValue).IsValid() || !fKey->IsValid() || !fVal->IsValid() ) {
                  return 0;
               }
               fPointers |= 0 != (fKey->fCase&kIsPointer);
               if (fPointers || (0 != (fKey->fProperties&kNeedDelete))) {
                  fProperties |= kNeedDelete;
               }
               if ( 0 == fValOffset )  {
                  fValOffset = alignedSize(fKey->fSize, (*fValue).fType.GetClass());
               }
               if ( 0 == fValDiff )  {
                  fValDiff = alignedSize(fValOffset + fVal->fSize, (*fValue).fType.GetClass());
               }
               if (num > 3 && !inside[3].empty()) {
                  if (! TClassEdit::IsDefAlloc(inside[3].c_str(),inside[0].c_str())) {
                     fProperties |= kCustomAlloc;
                  }
               }
               break;
            case ROOT::kSTLbitset:
               inside[1] = "bool";
               // Intentional fall through
            default:
               fValue = new Value(inside[1],silent);
               fVal   = new Value(*fValue);
               if ( !(*fValue).IsValid() || !fVal->IsValid() ) {
                  return 0;
               }
               if ( 0 == fValDiff )  {
                  fValDiff  = fVal->fSize;
                  // No need to align, the size even for a class should already
                  // be correctly padded for use in a vector.
               }
               if (num > 2 && !inside[2].empty()) {
                  if (! TClassEdit::IsDefAlloc(inside[2].c_str(),inside[0].c_str())) {
                     fProperties |= kCustomAlloc;
                  }
               }
               break;
         }
         fPointers |= 0 != (fVal->fCase&kIsPointer);
         if (fPointers || (0 != (fVal->fProperties&kNeedDelete))) {
            fProperties |= kNeedDelete;
         }
         fClass = cl;
         return this;
      }
      Fatal("TEmulatedCollectionProxy","Components of %s not analysed!",cl->GetName());
   }
   Fatal("TEmulatedCollectionProxy","Collection class %s not found!",fTypeinfo.name());
   return 0;
}
 
Bool_t TEmulatedCollectionProxy::IsValid() const
{
   // Return true if the collection proxy was well initialized.
   return  (0 != fCreateEnv.call);
}
 
UInt_t TEmulatedCollectionProxy::Size() const
{
   // Return the current size of the container
 
   if ( fEnv && fEnv->fObject )   {
      return fEnv->fSize = PCont_t(fEnv->fObject)->size()/fValDiff;
   }
   Fatal("TEmulatedCollectionProxy","Size> Logic error - no proxy object set.");
   return 0;
}
 
void TEmulatedCollectionProxy::Clear(const char* opt)
{
   // Clear the emulated collection.
   Resize(0, opt && *opt=='f');
}
 
void TEmulatedCollectionProxy::Shrink(UInt_t nCurr, UInt_t left, Bool_t force )
{
   // Shrink the container
 
   typedef std::string String_t;
   char* addr  = ((char*)fEnv->fStart) + fValDiff*left;
   size_t i;
 
   switch ( fSTL_type )  {
      case ROOT::kSTLmap:
      case ROOT::kSTLmultimap:
         addr = ((char*)fEnv->fStart) + fValDiff*left;
         switch(fKey->fCase)  {
            case kIsFundamental:  // Only handle primitives this way
            case kIsEnum:
               break;
            case kIsClass:
               for( i= fKey->fType ? left : nCurr; i<nCurr; ++i, addr += fValDiff ) {
                  // Call emulation in case non-compiled content
                  fKey->fType->Destructor(addr, kTRUE);
               }
               break;
            case kBIT_ISSTRING:
               for( i=left; i<nCurr; ++i, addr += fValDiff ) {
                  ((std::string*)addr)->~String_t();
               }
               break;
            case kIsPointer|kIsClass:
               for( i=left; i<nCurr; ++i, addr += fValDiff )  {
                  StreamHelper* h = (StreamHelper*)addr;
                  //Eventually we'll need to delete this
                  //(but only when needed).
                  void* ptr = h->ptr();
                  if (force) fKey->fType->Destructor(ptr);
                  h->set(0);
               }
               break;
            case 0U|kIsPointer|kBIT_ISSTRING:
               for( i=nCurr; i<left; ++i, addr += fValDiff )   {
                  StreamHelper* h = (StreamHelper*)addr;
                  //Eventually we'll need to delete this
                  //(but only when needed).
                  if (force) delete (std::string*)h->ptr();
                  h->set(0);
               }
               break;
            case 0U|kIsPointer|kBIT_ISTSTRING|kIsClass:
               for( i=nCurr; i<left; ++i, addr += fValDiff )   {
                  StreamHelper* h = (StreamHelper*)addr;
                  if (force) delete (TString*)h->ptr();
                  h->set(0);
               }
               break;
         }
         addr = ((char*)fEnv->fStart)+fValOffset+fValDiff*left;
         // DO NOT break; just continue
 
         // General case for all values
      default:
         switch( fVal->fCase )  {
            case kIsFundamental:  // Only handle primitives this way
            case kIsEnum:
               break;
            case kIsClass:
               for( i=left; i<nCurr; ++i, addr += fValDiff )  {
                  // Call emulation in case non-compiled content
                  fVal->fType->Destructor(addr,kTRUE);
               }
               break;
            case kBIT_ISSTRING:
               for( i=left; i<nCurr; ++i, addr += fValDiff )
                  ((std::string*)addr)->~String_t();
               break;
            case kIsPointer|kIsClass:
               for( i=left; i<nCurr; ++i, addr += fValDiff )  {
                  StreamHelper* h = (StreamHelper*)addr;
                  void* p = h->ptr();
                  if ( p && force )  {
                     fVal->fType->Destructor(p);
                  }
                  h->set(0);
               }
               break;
            case 0U|kIsPointer|kBIT_ISSTRING:
               for( i=nCurr; i<left; ++i, addr += fValDiff )   {
                  StreamHelper* h = (StreamHelper*)addr;
                  if (force) delete (std::string*)h->ptr();
                  h->set(0);
               }
               break;
            case 0U|kIsPointer|kBIT_ISTSTRING|kIsClass:
               for( i=nCurr; i<left; ++i, addr += fValDiff )   {
                  StreamHelper* h = (StreamHelper*)addr;
                  if (force) delete (TString*)h->ptr();
                  h->set(0);
               }
               break;
         }
   }
   WithCont(fEnv->fObject, [&](auto *c, std::size_t alignmentElemSize) {
      assert(fValDiff % alignmentElemSize == 0);
      c->resize(left * fValDiff / alignmentElemSize);
      fEnv->fStart = left > 0 ? c->data() : nullptr;
   });
   return;
}
 
void TEmulatedCollectionProxy::Expand(UInt_t nCurr, UInt_t left)
{
   // Expand the container
   size_t i;
   void *oldstart = fEnv->fStart;
   WithCont(fEnv->fObject, [&](auto *c, std::size_t alignmentElemSize) {
      assert(fValDiff % alignmentElemSize == 0);
      c->resize(left * fValDiff / alignmentElemSize);
      fEnv->fStart = left > 0 ? c->data() : nullptr;
   });
 
   char* addr = ((char*)fEnv->fStart) + fValDiff*nCurr;
   switch ( fSTL_type )  {
      case ROOT::kSTLmap:
      case ROOT::kSTLmultimap:
         switch(fKey->fCase)  {
            case kIsFundamental:  // Only handle primitives this way
            case kIsEnum:
               break;
            case kIsClass:
               if (oldstart && oldstart != fEnv->fStart) {
                  Long_t offset = 0;
                  for( i=0; i<=nCurr; ++i, offset += fValDiff ) {
                     // For now 'Move' only register the change of location
                     // so per se this is wrong since the object are copied via memcpy
                     // rather than a copy (or move) constructor.
                     fKey->fType->Move(((char*)oldstart)+offset,((char*)fEnv->fStart)+offset);
                  }
               }
               for( i=nCurr; i<left; ++i, addr += fValDiff )
                  fKey->fType->New(addr);
               break;
            case kBIT_ISSTRING:
               for( i=nCurr; i<left; ++i, addr += fValDiff )
                  ::new(addr) std::string();
               break;
            case kIsPointer|kIsClass:
            case 0U|kIsPointer|kBIT_ISSTRING:
            case 0U|kIsPointer|kBIT_ISTSTRING|kIsClass:
               for( i=nCurr; i<left; ++i, addr += fValDiff )
                  *(void**)addr = 0;
               break;
         }
         addr = ((char*)fEnv->fStart)+fValOffset+fValDiff*nCurr;
         // DO NOT break; just continue
 
         // General case for all values
      default:
         switch(fVal->fCase)  {
            case kIsFundamental:  // Only handle primitives this way
            case kIsEnum:
               break;
            case kIsClass:
               if (oldstart && oldstart != fEnv->fStart) {
                  Long_t offset = 0;
                  for( i=0; i<=nCurr; ++i, offset += fValDiff ) {
                     // For now 'Move' only register the change of location
                     // so per se this is wrong since the object are copied via memcpy
                     // rather than a copy (or move) constructor.
                     fVal->fType->Move(((char*)oldstart)+offset,((char*)fEnv->fStart)+offset);
                  }
               }
               for( i=nCurr; i<left; ++i, addr += fValDiff ) {
                  fVal->fType->New(addr);
               }
               break;
            case kBIT_ISSTRING:
               for( i=nCurr; i<left; ++i, addr += fValDiff )
                  ::new(addr) std::string();
               break;
            case kIsPointer|kIsClass:
            case 0U|kIsPointer|kBIT_ISSTRING:
            case 0U|kIsPointer|kBIT_ISTSTRING|kIsClass:
               for( i=nCurr; i<left; ++i, addr += fValDiff )
                  *(void**)addr = 0;
               break;
         }
         break;
   }
}
 
void TEmulatedCollectionProxy::Resize(UInt_t left, Bool_t force)
{
   // Resize the container
 
   if ( fEnv && fEnv->fObject )   {
      size_t nCurr = Size();
      PCont_t c = PCont_t(fEnv->fObject);
      fEnv->fStart = nCurr > 0 ? c->data() : 0;
      if ( left == nCurr )  {
         return;
      }
      else if ( left < nCurr )  {
         Shrink(nCurr, left, force);
         return;
      }
      Expand(nCurr, left);
      return;
   }
   Fatal("TEmulatedCollectionProxy","Resize> Logic error - no proxy object set.");
}
 
void* TEmulatedCollectionProxy::At(UInt_t idx)
{
   // Return the address of the value at index 'idx'
   if ( fEnv && fEnv->fObject )   {
      PCont_t c = PCont_t(fEnv->fObject);
      size_t  s = c->size();
      if ( idx >= (s/fValDiff) )  {
         return 0;
      }
      return idx < (s / fValDiff) ? c->data() + idx * fValDiff : 0;
   }
   Fatal("TEmulatedCollectionProxy","At> Logic error - no proxy object set.");
   return 0;
}
 
void* TEmulatedCollectionProxy::Allocate(UInt_t n, Bool_t forceDelete)
{
   // Allocate the necessary space.
 
   Resize(n, forceDelete);
   return fEnv->fObject;
}
 
////////////////////////////////////////////////////////////////////////////////
/// Insert data into the container where data is a C-style array of the actual type contained in the collection
/// of the given size.   For associative container (map, etc.), the data type is the pair<key,value>.
 
void TEmulatedCollectionProxy::Insert(const void * /* data */, void * /*container*/, size_t /*size*/)
{
   Fatal("Insert","Not yet implemented, require copy of objects.");
}
 
void TEmulatedCollectionProxy::Commit(void* /* env */ )
{
}
 
void TEmulatedCollectionProxy::ReadItems(int nElements, TBuffer &b)
{
   // Object input streamer
   Bool_t vsn3 = b.GetInfo() && b.GetInfo()->GetOldVersion()<=3;
   StreamHelper* itm = (StreamHelper*)At(0);
   switch (fVal->fCase) {
      case kIsFundamental:  //  Only handle primitives this way
      case kIsEnum:
         switch( int(fVal->fKind) )   {
            case kBool_t:    b.ReadFastArray(&itm->boolean   , nElements); break;
            case kChar_t:    b.ReadFastArray(&itm->s_char    , nElements); break;
            case kShort_t:   b.ReadFastArray(&itm->s_short   , nElements); break;
            case kInt_t:     b.ReadFastArray(&itm->s_int     , nElements); break;
            case kLong_t:    b.ReadFastArray(&itm->s_long    , nElements); break;
            case kLong64_t:  b.ReadFastArray(&itm->s_longlong, nElements); break;
            case kFloat_t:   b.ReadFastArray(&itm->flt       , nElements); break;
            case kFloat16_t: b.ReadFastArrayFloat16(&itm->flt, nElements); break;
            case kDouble_t:  b.ReadFastArray(&itm->dbl       , nElements); break;
            case kUChar_t:   b.ReadFastArray(&itm->u_char    , nElements); break;
            case kUShort_t:  b.ReadFastArray(&itm->u_short   , nElements); break;
            case kUInt_t:    b.ReadFastArray(&itm->u_int     , nElements); break;
            case kULong_t:   b.ReadFastArray(&itm->u_long    , nElements); break;
            case kULong64_t: b.ReadFastArray(&itm->u_longlong, nElements); break;
            case kDouble32_t:b.ReadFastArrayDouble32(&itm->dbl,nElements); break;
            case kchar:
            case kNoType_t:
            case kOther_t:
               Error("TEmulatedCollectionProxy","fType %d is not supported yet!\n",fVal->fKind);
         }
         break;
 
#define DOLOOP(x) {int idx=0; while(idx<nElements) {StreamHelper* i=(StreamHelper*)(((char*)itm) + fValDiff*idx); { x ;} ++idx;} break;}
 
      case kIsClass:
         DOLOOP( b.StreamObject(i,fVal->fType) );
      case kBIT_ISSTRING:
         DOLOOP( i->read_std_string(b) );
      case kIsPointer|kIsClass:
         DOLOOP( i->read_any_object(fVal,b) );
      case 0U|kIsPointer|kBIT_ISSTRING:
         DOLOOP( i->read_std_string_pointer(b) );
      case 0U|kIsPointer|kBIT_ISTSTRING|kIsClass:
         DOLOOP( i->read_tstring_pointer(vsn3,b) );
   }
 
#undef DOLOOP
 
}
 
void TEmulatedCollectionProxy::WriteItems(int nElements, TBuffer &b)
{
   // Object output streamer
   StreamHelper* itm = (StreamHelper*)At(0);
   switch (fVal->fCase) {
      case kIsFundamental:  // Only handle primitives this way
      case kIsEnum:
         itm = (StreamHelper*)At(0);
            switch( int(fVal->fKind) )   {
            case kBool_t:    b.WriteFastArray(&itm->boolean   , nElements); break;
            case kChar_t:    b.WriteFastArray(&itm->s_char    , nElements); break;
            case kShort_t:   b.WriteFastArray(&itm->s_short   , nElements); break;
            case kInt_t:     b.WriteFastArray(&itm->s_int     , nElements); break;
            case kLong_t:    b.WriteFastArray(&itm->s_long    , nElements); break;
            case kLong64_t:  b.WriteFastArray(&itm->s_longlong, nElements); break;
            case kFloat_t:   b.WriteFastArray(&itm->flt       , nElements); break;
            case kFloat16_t: b.WriteFastArrayFloat16(&itm->flt, nElements); break;
            case kDouble_t:  b.WriteFastArray(&itm->dbl       , nElements); break;
            case kUChar_t:   b.WriteFastArray(&itm->u_char    , nElements); break;
            case kUShort_t:  b.WriteFastArray(&itm->u_short   , nElements); break;
            case kUInt_t:    b.WriteFastArray(&itm->u_int     , nElements); break;
            case kULong_t:   b.WriteFastArray(&itm->u_long    , nElements); break;
            case kULong64_t: b.WriteFastArray(&itm->u_longlong, nElements); break;
            case kDouble32_t:b.WriteFastArrayDouble32(&itm->dbl,nElements); break;
            case kchar:
            case kNoType_t:
            case kOther_t:
               Error("TEmulatedCollectionProxy","fType %d is not supported yet!\n",fVal->fKind);
         }
         break;
#define DOLOOP(x) {int idx=0; while(idx<nElements) {StreamHelper* i=(StreamHelper*)(((char*)itm) + fValDiff*idx); { x ;} ++idx;} break;}
      case kIsClass:
         DOLOOP( b.StreamObject(i,fVal->fType) );
      case kBIT_ISSTRING:
         DOLOOP( TString(i->c_str()).Streamer(b) );
      case kIsPointer|kIsClass:
         DOLOOP( b.WriteObjectAny(i->ptr(),fVal->fType) );
      case 0U|kBIT_ISSTRING|kIsPointer:
         DOLOOP( i->write_std_string_pointer(b) );
      case 0U|kBIT_ISTSTRING|kIsClass|kIsPointer:
         DOLOOP( i->write_tstring_pointer(b) );
   }
#undef DOLOOP
}
 
void TEmulatedCollectionProxy::ReadBuffer(TBuffer &b, void *obj, const TClass *onfileClass)
{
   // Read portion of the streamer.
 
   SetOnFileClass((TClass*)onfileClass);
   ReadBuffer(b,obj);
}
 
void TEmulatedCollectionProxy::ReadBuffer(TBuffer &b, void *obj)
{
   // Read portion of the streamer.
 
   TPushPop env(this,obj);
   int nElements = 0;
   b >> nElements;
   if ( fEnv->fObject )  {
      Resize(nElements,true);
   }
   if ( nElements > 0 )  {
      ReadItems(nElements, b);
   }
}
 
void TEmulatedCollectionProxy::Streamer(TBuffer &b)
{
   // TClassStreamer IO overload
   if ( b.IsReading() ) {  //Read mode
      int nElements = 0;
      b >> nElements;
      if ( fEnv->fObject )  {
         Resize(nElements,true);
      }
      if ( nElements > 0 )  {
         ReadItems(nElements, b);
      }
   }
   else {     // Write case
      int nElements = fEnv->fObject ? Size() : 0;
      b << nElements;
      if ( nElements > 0 )  {
         WriteItems(nElements, b);
      }
   }
}