c++11 Any

#include <iostream>
#include <string>
#include <type_traits>
#include <utility>
#include <stdexcept>
#include <typeindex>
#include <exception>
using namespace std;

struct Any
{
    Any(void) : m_tpIndex(std::type_index(typeid(void))) {}
    Any(const Any& that) : m_ptr(that.Clone()), m_tpIndex(that.m_tpIndex) {}
    Any(Any && that) : m_ptr(std::move(that.m_ptr)), m_tpIndex(that.m_tpIndex) {}

    //创建智能指针时，对于一般的类型，通过std::decay来移除引用和cv符，从而获取原始类型
    template<typename U, class = typename std::enable_if<!std::is_same<typename std::decay<U>::type, Any>::value, U>::type> 
    Any(U && value) 
        : m_ptr(new Derived < typename std::decay<U>::type>(std::forward<U>(value)))
        , m_tpIndex(std::type_index(typeid(typename std::decay<U>::type))) {}

    bool IsNull() const { return !bool(m_ptr); }

    template<class U> bool Is() const
    {
        return m_tpIndex == std::type_index(typeid(U));
    }

    //将Any转换为实际的类型
    template<class U>
    U& AnyCast()
    {
        if (!Is<U>())
        {
            std::cout << "can not cast " << typeid(U).name() << " to " << m_tpIndex.name() << std::endl;
            //throw std::logic_error{ "bad cast" };
        } 
        else {
            auto derived = dynamic_cast<Derived<U>*> (m_ptr.get());
            return derived->m_value;
        }
    }

    Any& operator=(const Any& a)
    {
        if (m_ptr == a.m_ptr)
            return *this;

        m_ptr = a.Clone();
        m_tpIndex = a.m_tpIndex;
        return *this;
    }

private:
    struct Base;
    typedef std::unique_ptr<Base> BasePtr;

    struct Base
    {
        virtual ~Base() {}
        virtual BasePtr Clone() const = 0;
    };

    template<typename T>
    struct Derived : Base
    {
        template<typename U>
        Derived(U && value) : m_value(std::forward<U>(value)) { }

        BasePtr Clone() const
        {
            return BasePtr(new Derived<T>(m_value));
        }

        T m_value;
    };

    BasePtr Clone() const
    {
        if (m_ptr != nullptr)
            return m_ptr->Clone();

        return nullptr;
    }

    BasePtr m_ptr;
    std::type_index m_tpIndex;
};


int main(int argc, char *argv[])
{
    map<string, Any> one;
    one["one"] = 1;
    one["two"] = 1.2;
    one["three"] = "hello";
    one["four"] = string("word");
    vector<int> two = { 1, 2, 3, 4, 5 };
    one["five"] = two;

    cout << one["one"].AnyCast<int>() << endl;
    cout << one["two"].AnyCast<double>() << endl;
    cout << one["three"].AnyCast<const char*>() << endl;
    cout << one["four"].AnyCast<string>() << endl;
    
    vector<int> tmp = one["five"].AnyCast< vector<int> >();
    for (auto it = tmp.begin(); it != tmp.end(); ++it) {
        cout << *it << endl;
    }

    getchar();
    return 0;
}