core: Explicitly instantiate some Callback class and function templates

src/core/model/object-base.cc

@@ -35,6 +35,10 @@
 
 namespace ns3
 {
+// Explicit instantiation declaration
+template Callback<ObjectBase*> MakeCallback<ObjectBase*>(ObjectBase* (*)());
+template Callback<ObjectBase*>::Callback();
+template class CallbackImpl<ObjectBase*>;
 
 NS_LOG_COMPONENT_DEFINE("ObjectBase");
 

src/core/model/object-base.h

@@ -335,6 +335,15 @@ class ObjectBase
                const AttributeValue& value);
 };
 
+// The following explicit template instantiation declarations prevent all the translation
+// units including this header file to implicitly instantiate the callbacks class and
+// function templates having ObjectBase as template type parameter that are required to be
+// instantiated more often (accorging to the ClangBuildAnalyzer tool).
+// These classes and functions are explicitly instantiated in object-base.cc
+extern template Callback<ObjectBase*> MakeCallback<ObjectBase*>(ObjectBase* (*)());
+extern template Callback<ObjectBase*>::Callback();
+extern template class CallbackImpl<ObjectBase*>;
+
 } // namespace ns3
 
 #endif /* OBJECT_BASE_H */