Custom Cast() function with templates

[Josh]

I'm trying to create a simpler Cast() function:

template <class T>
shared_ptr<T> Cast(shared_ptr<SharedObject> o);

Function definition:

	template <class T>
	shared_ptr<T> Cast(shared_ptr<SharedObject> o)
	{
#ifdef DEBUG
		return dynamic_pointer_cast<T>(o);
#else
		return static_pointer_cast<T>(o);
#endif
	}

But whenever I try to use it I get an unresolved external symbol error:

shared_ptr<Entity> entity = CreateBox();
shared_ptr<Model> model = Cast<Model>(entity);

I'm basically just wrapping dynamic_pointer_cast. Here is that function's definition:

template<class _Ty1,
	class _Ty2>
	shared_ptr<_Ty1> dynamic_pointer_cast(const shared_ptr<_Ty2>& _Other) _NOEXCEPT
	{	// dynamic_cast for shared_ptr that properly respects the reference count control block
	const auto _Ptr = dynamic_cast<typename shared_ptr<_Ty1>::element_type *>(_Other.get());

	if (_Ptr)
		{
		return (shared_ptr<_Ty1>(_Other, _Ptr));
		}

	return (shared_ptr<_Ty1>());
	}

 

[Josh]

This does not work either.

template <class T, class Y>
shared_ptr<T> Cast(shared_ptr<Y> o);

 

[thehankinator]

I don't know what the signature of CreateBox() is nor what Entity and Model classes look like but this compiles for me under VS2015 and MinGW 5.3.0 (Debug and Release for both). Entity had to have a virtual function to make it polymorphic.

#include <memory>

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

class Model : public Entity
{
public:
	virtual ~Model()
	{}
};


template <class T, class Y>
std::shared_ptr<T> Cast(std::shared_ptr<Y> o)
{
#ifdef DEBUG
	return std::dynamic_pointer_cast<T>(o);
#else
	return std::static_pointer_cast<T>(o);
#endif
}

std::shared_ptr<Entity> CreateBox()
{
	return std::dynamic_pointer_cast<Entity>(std::make_shared<Model>());
}

int main()
{
	std::shared_ptr<Entity> entity = CreateBox();
	std::shared_ptr<Model> model = Cast<Model>(entity);

	return 0;
}