from key to function ptr

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#include <iostream>
#include <unordered_map>
#include <map>
#include <functional>
#include <vector>

using namespace std;

enum A {
    RGB=3, YUV=2, GRAY=4
};

template<A t, A tt>
void f() {
    cout << "default" << endl;
    cout << t << endl;
    cout << tt << endl;
}

template<>
void f<A::RGB, A::YUV>() {
    cout << "spec rgb -> yuv" << endl;
}

template<>
void f<A::YUV, A::RGB>() {
    cout << "spec yuv -> rgb" << endl;
}

template<>
void f<A::YUV, A::GRAY>() {
    cout << "spec yuv -> gray" << endl;
}


int main()
{
    f<YUV,RGB>(); // yuv -> rgb
    std::vector<std::pair<std::pair<A,A>, std::function<void()>> > vec;
    vec.push_back(make_pair(make_pair(A::RGB, A::YUV), f<A::RGB,A::YUV>));
    vec.push_back(make_pair(make_pair(A::YUV, A::GRAY), f<A::YUV,A::GRAY>));
    vec.push_back(make_pair(make_pair(A::YUV, A::RGB), f<A::YUV,A::RGB>));
    auto functor = vec[0].second;
    functor(); // rgb->yuv
    
    for (auto iter = vec.begin(); iter != vec.end(); iter++) {
        if (iter->first == make_pair(A::YUV,A::GRAY)) {
            (iter->second)(); // yuv -> gray
            break;
        }
    }
    cout << "split" << endl;
    
    std::map<std::pair<A,A>, void(*)()> mmap;
    mmap.emplace(make_pair(RGB, YUV), f<RGB,YUV>);
    mmap.emplace(make_pair(YUV, GRAY), f<YUV,GRAY>);
    
    mmap[make_pair(YUV,GRAY)]();
    
    

    return 0;
}