I have an array std::array<T, N> arr for some T, N and I’d like to get an array of reference over arr‘s elements like so std::array<std::reference_wrapper<T>, N> arr_ref.
But as a reference needs to be set at its initialization, I did not work out a solution.
Therefore I would like to do something like that:
std::array<std::reference_wrapper<T>, N> ref{}
for (std::size_t i{0}; i < N; ++i)
ref[i] = arr[i];
But at compile-time and at the initialization of ref.
I thought of using some variadic template magic to convert my initial array to a parameter pack and then take a reference to each element but I am not sure this is possible.
My last option would be an array of raw ptrs or of std::optional<std::reference_wrapper<T>>.
>Solution :
#include <array>
#include <functional>
#include <utility>
#include <cstddef>
template<typename x_Item, ::std::size_t x_count, ::std::size_t... x_index___>
auto wrap_impl(::std::array<x_Item, x_count> & items, ::std::index_sequence<x_index___...>)
{
return ::std::array<::std::reference_wrapper<x_Item>, x_count>{items[x_index___]...};
}
template<typename x_Item, ::std::size_t x_count>
auto wrap(::std::array<x_Item, x_count> & items)
{
return wrap_impl(items, ::std::make_index_sequence<x_count>{});
}
#include <iostream>
int main()
{
::std::array items{1, 2, 3};
auto wrapped_items{wrap(items)};
for (auto & wrapped_item: wrapped_items)
{
::std::cout << wrapped_item.get() << ::std::endl;
}
return 0;
}