Method ReusableStringStream

tests/include/catch.hpp:13781–13784

    };

    ReusableStringStream::ReusableStringStream()
    :   m_index( Singleton<StringStreams>::getMutable().add() ),
        m_oss( Singleton<StringStreams>::getMutable().m_streams[m_index].get() )
    {}

    ReusableStringStream::~ReusableStringStream() {
        static_cast<std::ostringstream*>( m_oss )->str("");