Method rend

Bcore/src/main/cpp/base/stringpiece.h:147–149

    return const_reverse_iterator(ptr_ + length_);
  }
  const_reverse_iterator rend() const {
    return const_reverse_iterator(ptr_);
  }

  size_type copy(char* buf, size_type n, size_type pos = 0) const {
    size_type ret = std::min(length_ - pos, n);