Reference over array into array of reference-CodePudding

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>>.

CodePudding user response：

#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;
}

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