[io] Make case values constant expressions (root-project#11148)

Current clang-16 from main complains: "case value is not a constant
expression". Even if that error is probably relaxed before Clang 16
is released early next year, there is really no point in converting
an integer into an enum just to get a numeric value back.

This is (intentionally) a partial revert of commit ac36d87. An
alternative solution appears to be replacing EProperty (which refers
to the enum type in TVirtualCollectionProxy) with ::EProperty from
TDictionary.h. However, since the enum values are used as a bit mask
and fCase is defined as UInt_t anyhow, it makes more sense to compare
integer constants from the start.

Closes root-project#11128

Author: hahnjo

io/io/src/TGenCollectionStreamer.cxx

@@ -389,13 +389,13 @@ void TGenCollectionStreamer::ReadObjects(int nElements, TBuffer &b, const TClass
          switch (fVal->fCase) {
             case kIsClass:
                DOLOOP(b.StreamObject(i, fVal->fType, onFileValClass ));
-            case EProperty(kBIT_ISSTRING):
+            case kBIT_ISSTRING:
                DOLOOP(i->read_std_string(b));
-            case EProperty(kIsPointer | kIsClass):
+            case kIsPointer | kIsClass:
                DOLOOP(i->set(b.ReadObjectAny(fVal->fType)));
-            case EProperty(kIsPointer | kBIT_ISSTRING):
+            case kIsPointer | kBIT_ISSTRING:
                DOLOOP(i->read_std_string_pointer(b));
-            case EProperty(kIsPointer | kBIT_ISTSTRING | kIsClass):
+            case kIsPointer | kBIT_ISTSTRING | kIsClass:
                DOLOOP(i->read_tstring_pointer(vsn3, b));
          }
 #undef DOLOOP
@@ -442,20 +442,20 @@ void TGenCollectionStreamer::ReadObjects(int nElements, TBuffer &b, const TClass
                fFeed(fEnv->fStart,fEnv->fObject,fEnv->fSize);
                fDestruct(fEnv->fStart,fEnv->fSize);
                break;
-            case EProperty(kBIT_ISSTRING):
+            case kBIT_ISSTRING:
                DOLOOP(i->read_std_string(b))
                fFeed(fEnv->fStart,fEnv->fObject,fEnv->fSize);
                fDestruct(fEnv->fStart,fEnv->fSize);
                break;
-            case EProperty(kIsPointer | kIsClass):
+            case kIsPointer | kIsClass:
                DOLOOP(i->set(b.ReadObjectAny(fVal->fType)));
                fFeed(fEnv->fStart,fEnv->fObject,fEnv->fSize);
                break;
-            case EProperty(kIsPointer | kBIT_ISSTRING):
+            case kIsPointer | kBIT_ISSTRING:
                DOLOOP(i->read_std_string_pointer(b))
                fFeed(fEnv->fStart,fEnv->fObject,fEnv->fSize);
                break;
-            case EProperty(kIsPointer | kBIT_ISTSTRING | kIsClass):
+            case kIsPointer | kBIT_ISTSTRING | kIsClass:
                DOLOOP(i->read_tstring_pointer(vsn3, b));
                fFeed(fEnv->fStart,fEnv->fObject,fEnv->fSize);
                break;
@@ -864,16 +864,16 @@ void TGenCollectionStreamer::ReadMap(int nElements, TBuffer &b, const TClass *on
             case kIsClass:
                b.StreamObject(i, v->fType);
                break;
-            case EProperty(kBIT_ISSTRING):
+            case kBIT_ISSTRING:
                i->read_std_string(b);
                break;
-            case EProperty(kIsPointer | kIsClass):
+            case kIsPointer | kIsClass:
                i->set(b.ReadObjectAny(v->fType));
                break;
-            case EProperty(kIsPointer | kBIT_ISSTRING):
+            case kIsPointer | kBIT_ISSTRING:
                i->read_std_string_pointer(b);
                break;
-            case EProperty(kIsPointer | kBIT_ISTSTRING | kIsClass):
+            case kIsPointer | kBIT_ISTSTRING | kIsClass:
                i->read_tstring_pointer(vsn3, b);
                break;
          }