Question

This is the scenario:

class Base {
public:
  typedef Base type;
};

class Derived: public Base {
public:
  typedef Derived type;
};

I want something like:

int main() {
  Base * bs = new Derived();

  decltype(*bs)::type newvar;
}

How can i do something like above to get the type of the Derived class without using static / dynamic cast ?

Answer 1

No you cannot do that.

C++ is statically typed language, which means a type has to be determined at compile time.
In the example bs doesn’t know what object type it’s pointing.
See a scenario below to make it clearer:

Base * bs = (bool)? new Base() : new Derived();

You have to rely on virtual mechanism or dynamic_cast for achieving your ultimate purpose.