Templated partial application call issues - c++

Question

For the upcoming Coursework in January, I started developing a small DirectX engine. To find out if there is a performance increase I wanted to try to not use any virtuals at all (I know that virtuals aren't all bad, but I just wanted to see if it is possible without them).
When I started playing around with a simple StateManager, it got hard to avoid virtuals, but this is my current approach:
#include <boost\function.hpp>
#include <boost\bind.hpp>
template <class Derived>
struct TBaseState {
bool update(float delta) {
return static_cast<Derived *>(this)->update(delta);
};
};
struct CTestState : TBaseState<CTestState> {
bool update(float delta) {
return true;
}
};
class StateManager
{
public:
template <class StateClass> static void setState(StateClass nextState)
{
m_funcptrUpdate = boost::bind(&TBaseState<StateClass>::update, boost::ref(nextState), _1);
}
static bool update(float delta)
{
return m_funcptrUpdate(delta);
}
protected:
private:
static boost::function<bool (float)> m_funcptrUpdate;
};
Visual Studio 2010's Intellisense seems to think everything is fine, but when I want to compile the program and test the StateManager with a very basic approach:
CTestState* t = new CTestState();
StateManager::setState(*t);
StateManager::update(0.0f);
The following error is thrown during linking phase:
error LNK2001: unresolved external symbol "private: static class boost::function<bool __cdecl(float)> StateManager::m_funcptrUpdate" (?m_funcptrUpdate#StateManager##0V?$function#$$A6A_NM#Z#boost##A)
So obviously he can't find the binded function, but how can I solve this issue? I get similar errors if I use boost::bind directly to some class. Since I am a computer science student I would also be interested in some insight or approaches without boost (e.g. bind1st, ...).
EDIT:
I was also thinking about using C++11 Variadic Templates, but one of the coursework requirements is to stick to VS2012.

Answer 1

Static class members need to be given storage. They're like extern variables. Add a definition to one of your .cpp files, outside of the class definition:
boost::function<bool (float)> StateManager::m_funcptrUpdate;
Also, in this code:
template <class StateClass> static void setState(StateClass nextState)
{
m_funcptrUpdate = boost::bind(&TBaseState<StateClass>::update,
boost::ref(nextState), _1);
}
You're maintaining storing a reference to the local variable nextState. That reference will be invalid after setState returns.