join.hh

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#ifndef JOIN_HH
#define JOIN_HH

#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <utility>

namespace detail {

template<typename Collection, typename Separator>
class Joiner
{
public:
        Joiner(Collection&& col_, Separator&& sep_)
                : col(std::forward<Collection>(col_))
                , sep(std::forward<Separator>(sep_))
        {
        }

        friend std::ostream& operator<<(std::ostream& os, const Joiner& joiner)
        {
                return joiner.execute(os);
        }

        [[nodiscard]] operator std::string() const
        {
                std::ostringstream os;
                execute(os);
                return os.str();
        }

private:
        template<typename OutputStream>
        OutputStream& execute(OutputStream& os) const
        {
                auto first = std::begin(col);
                auto last  = std::end  (col);
                if (first != last) {
                        goto print;
                        while (first != last) {
                                os << sep;
                print:  os << *first;
                                ++first;
                        }
                }
                return os;
        }

private:
        Collection col;
        Separator sep;
};

} // namespace detail


template<typename Collection, typename Separator>
[[nodiscard]] detail::Joiner<Collection, Separator> join(Collection&& col, Separator&& sep)
{
        return { std::forward<Collection>(col), std::forward<Separator>(sep) };
}

#endif