对临时工有约束力。l/r值

Whist从这个S/O编译以下代码 answer ,由于绑定问题,我不断出现错误。

class my_matrix {
  std::vector<std::vector<bool> >m;
public:
  my_matrix(unsigned int x, unsigned int y) {
    m.resize(x, std::vector<bool>(y,false));
  }
  class matrix_row {
    std::vector<bool>& row;
  public:
    matrix_row(std::vector<bool>& r) : row(r) {
    }
    bool& operator[](unsigned int y) {
      return row.at(y);
    }
  };
  matrix_row& operator[](unsigned int x) {
    return matrix_row(m.at(x));
  }
};
// Example usage
my_matrix mm(100,100);
mm[10][10] = true;

这是报告

m.cpp:16:14: error: non-const lvalue reference to type 'bool' cannot bind to a
      temporary of type 'reference' (aka '__bit_reference<std::__1::vector<bool,
      std::__1::allocator<bool> > >')
      return row.at(y);
             ^~~~~~~~~
m.cpp:20:12: error: non-const lvalue reference to type 'my_matrix::matrix_row'
      cannot bind to a temporary of type 'my_matrix::matrix_row'
    return matrix_row(m.at(x));
           ^~~~~~~~~~~~~~~~~~~

question 但我还是不知道该怎么办。

**编辑**

matrix_row& operator[](unsigned int x) {
    std::vector<int> e = m.at(x);
    matrix_row f = matrix_row(e);
    return f;

它没有。这似乎是用内存创建变量(e和f)?