Question

我正在尝试实现一个迭代器，该迭代器将逐行通过矩阵。

struct Matrix { 
    col_count: usize,
    backing: Vec<bool>
}

fn get_row_mut<'a>(&'a mut self, row: usize) -> &'a mut [bool] {
    &mut self.backing[row * self.col_count .. (row + 1) * self.col_count]
}

struct MatrixIterator<'a> {
    matrix: &'a mut Matrix,
    curr_row: usize
}

impl<'a> IntoIterator for &'a mut Matrix {
    type Item = &'a mut [bool];
    type IntoIter = MatrixIterator<'a>;

    fn into_iter(self) -> Self::IntoIter {
        MatrixIterator {matrix: self, curr_row: 0}
    }
}

impl<'b, 'a: 'b> Iterator for MatrixIterator<'a> {
    type Item = &'a mut [bool];
    fn next(&mut self) -> Option<Self::Item> {
        let row : &'b mut [bool] = self.matrix.get_row_mut(self.curr_row);
        if self.curr_row < self.matrix.row_count {
            Some(row)
        } else {
            None
        }
    }
}

出现错误：

error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
  --> src/matrix.rs:93:48
   |
93 |         let row : &'b mut [bool] = self.matrix.get_row_mut(self.curr_row);
   |                                                ^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 92:5...
  --> src/matrix.rs:92:5
   |
92 |     fn next(&mut self) -> Option<Self::Item> {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...so that reference does not outlive borrowed content
  --> src/matrix.rs:93:36
   |
93 |         let row : &'b mut [bool] = self.matrix.get_row_mut(self.curr_row);
   |                                    ^^^^^^^^^^^
note: but, the lifetime must be valid for the lifetime `'b` as defined on the impl at 90:6...
  --> src/matrix.rs:90:6
   |
90 | impl<'b, 'a: 'b> Iterator for MatrixIterator<'a> {
   |      ^^
note: ...so that reference does not outlive borrowed content
  --> src/matrix.rs:93:36
   |
93 |         let row : &'b mut [bool] = self.matrix.get_row_mut(self.curr_row);
   |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

首先，编译器是否正在尝试猜测get_row_mut返回的值的生存期？如果是这样，那么对于第一个冲突的要求，编译器关心的参考是哪个？另外，“一生难道不是一个完美的人选吗？”

error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
  --> src/matrix.rs:95:13
   |
95 |             Some(row)
   |             ^^^^^^^^^
   |
note: first, the lifetime cannot outlive the lifetime `'b` as defined on the impl at 90:6...
  --> src/matrix.rs:90:6
   |
90 | impl<'b, 'a: 'b> Iterator for MatrixIterator<'a> {
   |      ^^
note: ...so that reference does not outlive borrowed content
  --> src/matrix.rs:95:18
   |
95 |             Some(row)
   |                  ^^^
note: but, the lifetime must be valid for the lifetime `'a` as defined on the impl at 90:10...
  --> src/matrix.rs:90:10
   |
90 | impl<'b, 'a: 'b> Iterator for MatrixIterator<'a> {
   |          ^^
note: ...so that the types are compatible
  --> src/matrix.rs:92:46
   |
92 |       fn next(&mut self) -> Option<Self::Item> {
   |  ______________________________________________^
93 | |         let row : &'b mut [bool] = self.matrix.get_row_mut(self.curr_row);
94 | |         if self.curr_row < self.matrix.row_count {
95 | |             Some(row)
...  |
98 | |         }
99 | |     }
   | |_____^
   = note: expected `std::iter::Iterator`
              found `std::iter::Iterator`
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

对于此错误，我的处理过程为：Some(row)的生存期不应长于b'-这意味着它可以是b'。因此，现在我们有一个要求，即b'在寿命a'内有效。好吧，如果a'== b'，那也将是正确的。基本上Some(row)的生存期应该为== a'== b'并且似乎都满足了这两个要求，但是我看不见的逻辑应该存在一个缺陷

由于需求冲突，无法推断生命周期

0 个答案: