#include <iostream>
#include <algorithm>
#include <vector>
#include <type_traits>
// indicates that the type doesn't have a tag type (like pointers and standard iterators)
struct no_tag{};
namespace detail
{
template <typename T>
auto tag_helper(int) -> typename T::tag;
template <typename>
auto tag_helper(long) -> no_tag;
}
// get T::tag or no_tag if T::tag isn't defined.
template <typename T>
using tag_t = decltype(detail::tag_helper<T>(0));
namespace N
{
struct my_iterator_tag {};
struct A{ using tag = my_iterator_tag; };
struct B{ using tag = my_iterator_tag; };
struct C{ using tag = my_iterator_tag; };
}
namespace N
{
template<class SomeN1, class SomeN2>
SomeN2 copy_helper(SomeN1 first, SomeN1 last, SomeN2 d_first, no_tag)
{
std::cout << "calling std::copy\n";
return std::copy(std::forward<SomeN1>(first), std::forward<SomeN1>(last), std::forward<SomeN2>(d_first));
}
template<class SomeN1, class SomeN2>
SomeN2 copy_helper(SomeN1 first, SomeN1 last, SomeN2 d_first, my_iterator_tag)
{
// your custom copy
std::cout << "custom copy function\n";
return {};
}
template<class SomeN1, class SomeN2>
SomeN2 copy(SomeN1 first, SomeN1 last, SomeN2 d_first)
{
return copy_helper(std::forward<SomeN1>(first), std::forward<SomeN1>(last), std::forward<SomeN2>(d_first), tag_t<SomeN1>{});
}
}
template<class It1, class It2>
void do_something(It1 first, It1 second, It2 d_first)
{
N::copy(first, second, d_first);
}
int main()
{
N::A a1, a2, a3;
std::cout << "using custom iterator: ";
do_something(a1, a2, a3);
std::cout << "using vector iterator: ";
std::vector<int> v;
do_something(std::begin(v), std::end(v), std::begin(v));
std::cout << "using pointer: ";
int* ptr = new int[10];
do_something(ptr, ptr + 5, ptr);
return 0;
}
