Method substr

tutorials/external/catch.hpp:11495–11500

        }
    }
    auto StringRef::substr( size_type start, size_type size ) const noexcept -> StringRef {
        if( start < m_size )
            return StringRef( m_start+start, size );
        else
            return StringRef();
    }
    auto StringRef::operator == ( StringRef const& other ) const noexcept -> bool {
        return
            size() == other.size() &&