实现指针元组的深度复制

template<class T> T deep_copy(const T& t);
template<class T> T* deep_copy(T* tp);
template<class... Ts> std::tuple<Ts...> deep_copy(const std::tuple<Ts...>&);
template<class T>
T deep_copy(const T& t) { return t; }
template<class T>
T* deep_copy(T* tp) { return new T(deep_copy(*tp)); }
template<class... Ts, size_t... Is>
std::tuple<Ts...> deep_copy_impl(const std::tuple<Ts...>& t, std::index_sequence<Is...>) {
    return std::tuple<Ts...>{deep_copy(std::get<Is>(t))... };
}
template<class... Ts>
std::tuple<Ts...> deep_copy(const std::tuple<Ts...>& t) {
    return deep_copy_impl(tuple, std::index_sequence_for<Ts...>());
}

将T.C.的想法扩展到STL容器：

#include <iostream>
#include <type_traits>
#include <utility>
#include <tuple>
#include <vector>
#include <set>
template <typename T>
using void_t = void;
template <typename T, typename = void>
struct has_emplace_back : std::false_type {};
template <typename T>
struct has_emplace_back<T, void_t<decltype(std::declval<T>().emplace_back(std::declval<typename T::value_type>()))>> : std::true_type {};
template <typename T, typename = void>
struct has_emplace : std::false_type {};
template <typename T>
struct has_emplace<T, void_t<decltype(std::declval<T>().emplace(std::declval<typename T::value_type>()))>> : std::true_type {};
// etc... for other container types.
template <typename T>
struct is_stl_container : std::integral_constant<bool, has_emplace_back<T>::value || has_emplace<T>::value> {};
template <typename Container> std::enable_if_t<has_emplace_back<Container>::value, Container> deep_copy (const Container&);
template <typename Container> std::enable_if_t<has_emplace<Container>::value, Container> deep_copy (const Container&);
template <typename... Ts> std::tuple<Ts...> deep_copy (const std::tuple<Ts...>&);  // This forward declarations, though not needed to compile, is needed for the nested deep copying to work correctly.
template <typename T>
std::enable_if_t<!is_stl_container<T>::value, T> deep_copy (const T& t) {
    return t;
}
template <typename T>
T* deep_copy (T* t) {
    return new T(deep_copy(*t));  // Note that since T's copy constructor is called here, then if T is a custom class that has its own custom copy constructor that carries out deep copying, then t's pointer data members are also deep copied.
}
template <typename... Ts, std::size_t... Is>
std::tuple<Ts...> deep_copy_impl (const std::tuple<Ts...>& tuple, std::index_sequence<Is...>) {
    return std::tuple<Ts...>{ deep_copy(std::get<Is>(tuple))... };
}
template <typename... Ts>
std::tuple<Ts...> deep_copy (const std::tuple<Ts...>& tuple) {
    return deep_copy_impl(tuple, std::index_sequence_for<Ts...>{});
}
template <typename Container>
std::enable_if_t<has_emplace_back<Container>::value, Container> deep_copy (const Container& c) {
    Container container;
    for (const typename Container::value_type& t : c)
        container.emplace_back(deep_copy(t));
    return container;
}
template <typename Container>
std::enable_if_t<has_emplace<Container>::value, Container> deep_copy (const Container& c) {
    Container container;
    for (const typename Container::value_type& t : c)
        container.emplace(deep_copy(t));
    return container;
}
// Testing
template <typename Tuple, std::size_t... Is>
std::ostream& print_tuple_impl (const Tuple& tuple, std::ostream& os, std::index_sequence<Is...>) {
    const int a[] = {(os << "std::get<" << Is << ">(tuple) = " << std::get<Is>(tuple) << 'n', 0)...};
    static_cast<void>(a);
    return os;
}
template <typename Tuple>
std::ostream& print_tuple (const Tuple& tuple, std::ostream& os = std::cout) {
    return print_tuple_impl (tuple, os, std::make_index_sequence<std::tuple_size<Tuple>::value>{});
}
int main() {
    std::tuple<double*, bool*> t(new double(3.5), new bool(true));
    print_tuple(t);
    std::tuple<double*, bool*> n = t;
    print_tuple(n);
    std::cout << "Above is shallow copying only.nn";
    std::tuple<int*, std::tuple<double*, bool*>*, char> tup(new int(5), &t, 'a');
    print_tuple(tup);
    std::tuple<int*, std::tuple<double*, bool*>*, char> q = deep_copy(tup); 
    print_tuple(q);
    std::cout << "nAbove and below show that we have full deep copying:n";
    print_tuple(*std::get<1>(tup));
    print_tuple(*std::get<1>(q));
    std::cout << "nDeep copy of a vector of pointers:n";
    std::vector<int*> v = {new int(5), new int(2), new int(8)};
    for (int* x : v) std::cout << x << ' ';  std::cout << 'n';
    std::vector<int*> u = deep_copy(v);
    for (int* x : u) std::cout << x << ' ';  std::cout << 'n';
    std::cout << "nDeep copy of a set of pointers:n";
    std::set<int*> s = {new int(5), new int(2), new int(8)};
    for (int* x : s) std::cout << x << ' ';  std::cout << 'n';
    std::set<int*> ss = deep_copy(s);
    for (int* x : ss) std::cout << x << ' ';  std::cout << 'n';
}

输出：

std::get<0>(tuple) = 0x8513d0
std::get<1>(tuple) = 0x8513b0
std::get<0>(tuple) = 0x8513d0
std::get<1>(tuple) = 0x8513b0
Above is shallow copying only.
std::get<0>(tuple) = 0x8513f0
std::get<1>(tuple) = 0x72fd70
std::get<2>(tuple) = a
std::get<0>(tuple) = 0x851410
std::get<1>(tuple) = 0x851470
std::get<2>(tuple) = a
Above and below show that we have full deep copying:
std::get<0>(tuple) = 0x8513d0
std::get<1>(tuple) = 0x8513b0
std::get<0>(tuple) = 0x851430
std::get<1>(tuple) = 0x851450
Deep copy of a vector of pointers:
0x851490 0x8514b0 0x8514d0
0x851510 0x851550 0x851530
Deep copy of a set of pointers:
0x851570 0x8515c0 0x8515e0
0x851690 0x851800 0x851870