proxy sort

#include <iostream>
#include <iomanip>

#include <type_traits>
#include <utility>
#include <iterator>
#include <algorithm>
#include <deque>
#include <forward_list>

#include <cstdlib>
#include <cassert>

template< typename iterator >
void
proxy_sort(iterator beg, iterator end)
{
    static_assert(std::is_base_of< std::forward_iterator_tag, typename std::iterator_traits< iterator >::iterator_category >{});
    using reference = typename std::iterator_traits< iterator >::reference;
    using pointer = typename std::iterator_traits< iterator >::pointer;
    struct iterator_adaptor
    { // In `std::swap` makes first and last statement in `T tmp(std::move(lhs)); lhs = std::move(rhs); rhs = std::move(tmp);` a no-op.

        iterator_adaptor(reference value)
            : p(&value)
        { ; }

        iterator_adaptor(iterator_adaptor &&)
            : p(nullptr)
        { ; }

        void
        operator = (iterator_adaptor && rhs) &
        {
            if (!!rhs.p) {
                std::iter_swap(p, rhs.p);
            }
        }

        bool
        operator < (iterator_adaptor const & rhs) const
        {
            return (*p < *rhs.p);
        }

    private :

        pointer p;

    };
    std::deque< iterator_adaptor > proxy_(beg, end);
    std::sort(std::begin(proxy_), std::end(proxy_));
}

int
main()
{
    std::forward_list< int > l{5, 4, 3, 2, 1};
    std::copy(std::cbegin(l), std::cend(l), std::ostream_iterator< int >(std::cout, " ")); std::cout << std::endl;
    proxy_sort(std::begin(l), std::end(l));
    std::copy(std::cbegin(l), std::cend(l), std::ostream_iterator< int >(std::cout, " ")); std::cout << std::endl;
    return EXIT_SUCCESS;
}