C++實現的Tuple類，很是好用

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C++實現的Tuple類，很是好用，新老編譯器都支持。在編譯器支持可變模版參數的狀況下，這個Tuple支持任意多成員，不支持的狀況下，支持的成員是有限的，如今只支持3個成員，須要支持跟多成員，也能夠輕鬆擴展下。有碼有真相：

#include <iostream>
#include <typeinfo>

using namespace std;

#ifdef __GXX_EXPERIMENTAL_CXX0X__
template <typename... Rest> struct Tuple;
template <> struct Tuple<> {};

template <typename First, typename ... Rest>
struct Tuple<First, Rest...> : public Tuple<Rest...> {
    Tuple() : value() {}
    Tuple(First &&first, Rest&&... rest)
        : value(std::forward<First>(first))
        , Tuple<Rest...>(std::forward<Rest>(rest)...)
    {}
    First value;
};

template <size_t N, typename TP> struct Tuple_Element;

template <typename T, typename ... Rest>
struct Tuple_Element<0, Tuple<T, Rest...>> {
    typedef T type;
    typedef Tuple<T, Rest...> TPType;
};

template <size_t N, typename T, typename ... Rest>
struct Tuple_Element<N, Tuple<T, Rest...>>
    : public Tuple_Element<N - 1, Tuple<Rest...>>
{};

template <size_t N, typename ... Rest>
typename Tuple_Element<N, Tuple<Rest...>>::type& get(Tuple<Rest...> &tp) {
    typedef typename Tuple_Element<N, Tuple<Rest...>>::TPType type;
    return ((type &)tp).value;
}

#else

struct VoidType;

template <typename T1, typename T2, typename T3>
struct Tuple;

template <>
struct Tuple<VoidType, VoidType, VoidType> {
};

template <typename T1>
struct Tuple<T1, VoidType, VoidType> {
    Tuple()
    {}

    Tuple(const T1 &v1)
        : value(v1)
    {}

    T1 value;
};

template <typename T1, typename T2>
struct Tuple<T1, T2, VoidType>
    : public Tuple<T2, VoidType, VoidType>
{
    Tuple()
    {}

    Tuple(const T1 &v1, const T2 &v2)
        : value(v1)
        , Tuple<T2, VoidType, VoidType>(v2)
    {}

    T1 value;
};

template <typename T1 = VoidType, typename T2 = VoidType, typename T3 = VoidType>
struct Tuple
    : public Tuple<T2, T3, VoidType>
{
    Tuple(const T1 &v1, const T2 &v2, const T3 &v3)
        : value(v1)
        , Tuple<T2, T3, VoidType>(v2, v3)
    {}

    T1 value;
};

template <size_t N, typename T1, typename T2, typename T3>
struct Tuple_Element;

template <>
struct Tuple_Element<0, VoidType, VoidType, VoidType> {
};

template <typename T1, typename T2, typename T3>
struct Tuple_Element<0, T1, T2, T3> {
    typedef T1 type;
    typedef Tuple<T1, T2, T3> TPType;
};

template <size_t N, typename T1, typename T2, typename T3>
struct Tuple_Element
    : Tuple_Element<N - 1, T2, T3, VoidType>
{
};

template <size_t N, typename T1, typename T2, typename T3>
typename Tuple_Element<N, T1, T2, T3>::type& get(Tuple<T1, T2, T3> &tp) {
    typedef typename Tuple_Element<N, T1, T2, T3>::TPType type;
    return ((type &)tp).value;
}

#endif

int main() {
    Tuple<> tmp();
    //cout << typeid(get<0>(tmp)).name() << endl;
    Tuple<int, string, double> tp(3, "2", 1.);
    cout<<get<0>(tp) << " " << typeid(get<0>(tp)).name() <<endl;
    cout<<get<1>(tp) << " " << typeid(get<1>(tp)).name() <<endl;
    cout<<get<2>(tp) << " " << typeid(get<2>(tp)).name() <<endl;
    cout << ((Tuple<string, double> &)tp).value << endl;
    Tuple<int> ft1;
    Tuple<int, float> ft2;
    return 0;
}
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