Use std::is_base_of to subset STL container contents., C++ (vc++)

Use std::is_base_of to subset STL container contents.

// C++11

#include <iostream>
#include <type_traits>
#include <vector>

// Demonstrate use of template specialization and std::is_base_of to extract
// subsets of STL containers based on the value_type of the output container.
// Only items in the input container that can be cast or converted to the
// output container type are appended.

using namespace std;

class A
{
public:
  virtual ~A() { };
};

class AA : public A
{
public:
  virtual ~AA() { };
  int thing() const { return 42; }
};

class AB : public A
{
public:
  virtual ~AB() { };
  int thing() const { return 21; }
};

class B
{
public:
  B() { m_thing = -1; }
  B(const AA* aa) { m_thing = aa ? aa->thing() : 0; }

int thing() const { return m_thing; }

protected:
  int m_thing;
};

namespace internal
{

template<
  typename ContainerOut,
  typename ContainerIn,
  bool IsB
>
struct convertTo;

template<
  typename ContainerOut,
  typename ContainerIn
>
struct convertTo<ContainerOut, ContainerIn, false>
{
	static ContainerOut value(ContainerIn& container)
	{
		ContainerOut result;
		for (auto entry : container)
		{
      auto tmp = dynamic_cast<typename ContainerOut::value_type>(entry);
      if (tmp)
			{
				result.insert(result.end(), tmp);
			}
		}
		return result;
	};
};

template<
  typename ContainerOut,
  typename ContainerIn
>
struct convertTo<ContainerOut, ContainerIn, true>
{
	static ContainerOut value(ContainerIn& container)
	{
		ContainerOut result;
		for (auto y : container)
		{
			AA* x = dynamic_cast<AA*>(y);
			if (x)
			{
        typename ContainerOut::value_type b(x);
				result.push_back(b);
			}
		}
		return result;
	}
};

} // internal

template<
  typename ContainerOut,
  typename ContainerIn
>
ContainerOut convertTo(ContainerIn& container)
{
  return internal::convertTo<
    ContainerOut,
    ContainerIn,
    std::is_base_of<B, typename ContainerOut::value_type>::value
    >::value(container);
}

int main()
{
  AA aa;
  AB ab;
  vector<A*> in{ &aa, &ab };
  vector<B> out1;
  out1 = convertTo<std::vector<B>>(in);
  vector<AB*> out2;
  out2 = convertTo<std::vector<AB*>>(in);

cout
    << "aa's thing: " << aa.thing() << "\n"
    << "ab's thing: " << ab.thing() << "\n"
    << "in   size " << in.size() << "\n"
    << "out1 size " << out1.size() << "\n"
    << "out2 size " << out2.size() << "\n"
		<< "out1 first thing: " << out1[0].thing() << "\n"
		<< "out2 first thing: " << out2[0]->thing() << "\n";
  return 0;
}


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