::operator<<(std::set)

#include <ostream>
#include <set>

template<typename CharT, typename Traits, typename Key, typename Compare, typename Allocator>
inline std::basic_ostream<CharT, Traits>&
operator<<(std::basic_ostream<CharT, Traits>& stream, const std::set<Key, Compare, Allocator>& set) {

    stream << '{';

    if(!set.empty()) {

        auto iter = set.begin();

        stream << *iter;
        ++iter;

        while(iter != set.end()) {
            stream << ',' << *iter;
            ++iter;
        }

    }

    return stream << '}';

}