整数値をキーとしたstateパターンをtemplateで実現 ref: http://qiita.com/abedominal/items/73e2a9448330837ea6d6

main.cpp

#include <iostream>
#include <iomanip>
#include <cstdint>

using namespace std;

template <typename T>
class Singleton
{
protected:
    Singleton(){}
    Singleton(Singleton const&);
    ~Singleton(){}

    Singleton& operator=(Singleton const&);

public:
    static T* getInstance()
    {
        static T i;
        return &i;
    }
};

class IState
{
public:
    IState(){}
    virtual ~IState(){}
    virtual void action() = 0;
    virtual uint8_t getNextState() = 0;
};

template<uint8_t N> class State;
template<>
class State<0> :public IState, public Singleton<State<0> >
{
public:
    void action(){ cout << "State0" << endl; }
    uint8_t getNextState()
    {
        return 1;
    }
};
template<>
class State<1> :public IState, public Singleton<State<1> >
{
public:
    void action(){ cout << "State1" << endl; }
    uint8_t getNextState()
    {
        return 0;
    }
};

template<uint8_t N>
static void initialize(IState* s[])
{
    s[N - 1] = State<N - 1>::getInstance();
    initialize<N-1>(s);
}
template<>
static void initialize<0>(IState* s[])
{
    s[0] = State<0>::getInstance();
}

class StateMachine
{
public:
    static const int N = 2;
    StateMachine():cur_()
    {
        initialize<N>(states_);
    }
    void transit()
    {
        states_[cur_]->action();
        cur_ = states_[cur_]->getNextState();
    }
private:
    IState* states_[N];
    uint8_t cur_;
};


int main(int argv, char* argc[])
{
    StateMachine state;
    state.transit();
    state.transit();
    state.transit();
    return 0;
}