Reading the standard, in 5.2.7/6 we find that unless the target is an unambiguous base of the source, source must be a polymorphic type. Then in 10.3/1 Virtual functions support dynamic binding and objectoriented programming. A class that declares or inherits a virtual function is called a polymorphic class. In other words the standard doesn’t … Read more
Acyclic Visitor (pdf) is a great use of it.
type_index is “a simple wrapper for type_info which can be used as an index type in associative containers (23.4) and in unordered associative containers (23.5)”. If you use type_index instead of type_info*, you will free yourself from having to provide an explicit comparator in your maps. The only cost is that you need to #include … Read more
The compiler generates RTTI (Run-Time Type Information) metadata for published members, but not for public members (by default). The main effect of this is that the published properties of an object will appear in the Object Inspector at design time. I do not know if you are writing components, but if you do, you probably … Read more
Are you using g++ or some other compiler? In g++ RTTI is enabled by default IIRC, and you can disable it with -fno-rtti. To test whether it is active or not use dynamic_cast or typeid UPDATE I believe that HPUX’s aCC/aC++ also has RTTI on by default, and I am unaware of a way to … Read more
It’s not possible in general to pick arbitrary template parameters. However, the usual way you do it is this: template<int N> struct foo { static const int value = N; }; and for types template<typename T> struct foo { typedef T type; }; You can access it then as foo<39>::value or foo<int>::type. If you have … Read more
Yes, it will be correct to an extent. Template functions are implicitly inline, and static objects in inline functions are shared across all translation units. So, in every translation unit, you will get the address of the same static local variable for the call to type_id<Type>(). You are protected here from ODR violations by the … Read more
RTTI in Delphi is still not quite as full-featured as Reflection in .NET or other managed languages, because it is operating on compiled code, not an Intermediate Language (bytecode). However, it is a very similar concept, and the new RTTI system in Delphi 2010 brings it a lot closer to reflection, exposing an entire object-oriented … Read more
TL;DR; std::any holds a pointer to a static member function of a templated class. This function can perform many operations and is specific to a given type since the actual instance of the function depends on the template arguments of the class. The implementation of std::any in libstdc++ is not that complex, you can have … Read more
dynamic_cast works only on polymorphic types, i.e. classes containing virtual functions. In gcc you can dynamic_cast to void* but not from: struct S { virtual ~S() {} }; int main() { S* p = new S(); void* v = dynamic_cast<void*>(p); S* p1 = dynamic_cast<S*>(v); // gives an error }