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);
    }

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

#endif