A c++11 way to apply a map function to some tuples

Guegant Jean

/***** maptuple.cpp *****/

#include <tuple>
#include <iostream>
#include <functional>

template<int ...S> struct indexes{};

template<int N, int ...S> struct generate_indexes : generate_indexes<N - 1, N - 1, S...> {};

template<int ...S> struct generate_indexes<0, S...> {
	typedef indexes<S...> type;
};

/***** Apply a function to all the elements of a tuple *****/
template<template<class> class F, typename ...Args> class _apply_tuple
{
	private: 
	std::tuple<Args...>& _tuple;

	public:
		_apply_tuple(std::tuple<Args...>& tuple): _tuple(tuple) { }

		void operator()() {
			typedef typename generate_indexes<sizeof...(Args)>::type indexes;
			do_map((indexes()));
		}

		template<int ...S> void do_map(indexes<S...>) {
			_do_map(std::get<S>(_tuple) ...);
		}

		template<typename Arg> void _do_map(Arg arg) {
			F<Arg>::apply(arg);
		}

		template<typename Arg, typename ...Argz> void _do_map(Arg arg, Argz... args) {
			F<Arg>::apply(arg);
			_do_map(args...);
		}
};

template<template<class> class F, typename ...Args> inline void apply_tuple(std::tuple<Args...>& tuple)
{
	(_apply_tuple<F, Args...>(tuple))();
}


/***** Apply a function to all the elements of a tuple and create a new tuple from the return values *****/
template<template<class> class F, typename ...Args> class _map_tuple
{
	private: 
	std::tuple<Args...>& _tuple;

	public:
		_map_tuple(std::tuple<Args...>& tuple): _tuple(tuple) { }

		std::tuple<Args...> operator()() {
			typedef typename generate_indexes<sizeof...(Args)>::type indexes;
			return do_map((indexes()));
		}

		template<int ...S> std::tuple<Args...> do_map(indexes<S...>) {
			return std::make_tuple(F<Args>::apply(std::get<S>(_tuple)) ...);
		}
};

template<template<class> class F, typename ...Args> inline std::tuple<Args...> map_tuple(std::tuple<Args...>& tuple)
{
	return (_map_tuple<F, Args...>(tuple))();
}

/***** test.cpp *****/

#include <string>
#include <maptuple.hpp>

template<typename V> struct magicChange
{
	static V apply(V value)
	{
		return value;
	}
};

template<> struct magicChange<int>
{
	static int apply(int value)
	{
		return 2;
	}
};

template<> struct magicChange<std::string>
{
	static std::string apply(std::string value)
	{
		if (value == "boîte") 
		{
			return "bite";
		}
		else if (value == "coquilles")
		{
			return "couilles";
		}
		else 
		{
			return value;	
		}
	}
};


template<typename V> struct printer {
	static void apply(V value)
	{
		std::cout << value << " ";
	}
};

int main()
{
	auto car = std::make_tuple("J'ai", std::string("mangé"), "une", std::string("boîte"), "d'escargots", "mais", "j'ai", "oublié", "d'enlever", std::string("les"), 10, std::string("coquilles"));

	auto bus = map_tuple<magicChange>(car);	

	std::cout << "Après correction: " << std::endl;
	
	apply_tuple<printer>(bus);

	std::cout << std::endl;
}