なにこれたのしいきもい

tmpl.cpp

#include <iostream>


template <typename T>
class Operator
{

public:

    template <T left, T right>
    class Add
    {
    public:
        static const T result = left + right;
    };


    template <T left, T right>
    class Sub
    {
    public:
        static const T result = left - right;
    };


    template <T left, T right>
    class Mul
    {
    public:
        static const T result = left * right;
    };


    template <template <T, T> class Op, T... values>
    class Fold;


    template <template <T, T> class Op, T head, T... left>
    class Fold<Op, head, left...>
    {
    public:
        static const T result = Op<head, Fold<Op, left...>::result>::result;
    };


    template <template <T, T> class Op, T head>
    class Fold<Op, head>
    {
    public:
        static const T result = head;
    };
};


int main(const int argc, const char* const args[])
{
    typedef Operator<int> IntOp;
    
    std::cout << IntOp::Fold<IntOp::Add, 10, 20, 30>::result << std::endl;

    std::cout << IntOp::Fold<IntOp::Mul, 10, 20, 30>::result << std::endl;
    
    return 0;
}