remember how to get the memory layout exptected for oldObj->fObject

rules/02_coordinate_transformation/Event_v3_LinkDef.h

@@ -3,7 +3,7 @@
 #pragma link C++ class Event+;
 
 #pragma read sourceClass = "Event" source = "float fX; float fY" version = "[2]" targetClass = \
-   "Event" target = "fR" target = "fPhi" code = "{ newObj->SetFromEuclidian(onfile.fX, onfile.fY); }"
+   "Event" target = "fR" target = "fPhi" include = "iostream" code = "{ std::cout << offset_Onfile_Event_fX << std::endl; newObj->SetFromEuclidian(onfile.fX, onfile.fY); std::cout << oldObj->fClass->GetClassVersion() << std::endl; }"
 
 #endif
 

rules/02_coordinate_transformation/getOnDiskClass.C

@@ -0,0 +1,53 @@
+void getOnDiskClass()
+{
+   gSystem->Load("./libEvent_v3.so");
+
+   auto cl = TClass::GetClass("Event", true, true);
+   std::cout << "  ... TClass class version: " << cl->GetClassVersion() << std::endl;
+
+   auto f = TFile::Open("data.root");
+
+   // Get the streamer info directly from TClass:
+   auto versionedInfo = cl->GetStreamerInfo(2);
+   std::cout << "  ... versioned streamer info class version: " << versionedInfo->GetClassVersion() << std::endl;
+
+   // The versioned streamer info knows about the old _and_ the new layout
+   versionedInfo->GetElements()->ls();
+
+   // The first element is "Event@@2       @@alloc"
+   cl = versionedInfo->GetElement(0)->GetClassPointer();
+   std::cout << "  ... old class version: " << cl->GetClassVersion() << std::endl;
+
+   // The first element is "Event@@2       @@alloc"
+   cl = versionedInfo->GetElement(0)->GetClassPointer();
+   std::cout << "  ... old class version: " << cl->GetClassVersion() << std::endl;
+
+   // The data member offsets, however, are strange!
+   // These are the offsets expected for oldObj->fObject in the schema evolution snippet
+   std::cout << "TClass offset of fX and fY: " << cl->GetDataMemberOffset("fX") << " "
+                                               << cl->GetDataMemberOffset("fY")<< std::endl;
+
+//   for (auto si : TRangeDynCast<TStreamerInfo>(*f->GetStreamerInfoList())) {
+//      if (!si || (std::string(si->GetName()) != "Event"))
+//         continue;
+//
+//      std::cout << "  ... streamer info class version: " << si->GetClassVersion() << std::endl;
+//
+//      auto versionedInfo = cl->GetStreamerInfo(si->GetClassVersion());
+//      std::cout << "  ... versioned streamer info class version: " << versionedInfo->GetClassVersion() << std::endl;
+//
+//      // The versioned streamer info knows about the old _and_ the new layout
+//      versionedInfo->GetElements()->ls();
+//
+//      // The first element is "Event@@2       @@alloc"
+//      cl = versionedInfo->GetElement(0)->GetClassPointer();
+//      std::cout << "  ... old class version: " << cl->GetClassVersion() << std::endl;
+//
+//      // The data member offsets, however, are strange!
+//      // These are the offsets expected for oldObj->fObject in the schema evolution snippet
+//      std::cout << "TClass offset of fX and fY: " << cl->GetDataMemberOffset("fX") << " "
+//                                                  << cl->GetDataMemberOffset("fY")<< std::endl;
+//
+//      si->ls();
+//   }
+}

rules/03_update_private_member/README.md

@@ -0,0 +1 @@
+Can the schema update function somehow be a friend of the target class?