Cannot assign to self.pos because it is borrowed

help
1 
impl Parse {
  fn new(source: String) -> Self {
    Self {
      pos: 0,
      input: source,
    }
  }

  fn parse_nodes(&mut self) -> usize {
    for (index, char) in self.next_ele() {
      self.pos += 1
    }
    self.pos
  }
  fn next_ele(&self) -> CharIndices {
    self.input.char_indices()
  }
}

let mut v = Parse::new("<div><div></div></div>".to_string());
    let c = v.parse_nodes();
    println!("{}",c)

error: cannot assign to self.pos because it is borrowed

How can I make C normal print?

2

The error is due to the fact that next_ele puts a borrow of self into its return value - compiler doesn't try to check what it really needs to borrow, all that is checked is the signature. You can't mutate self while holding a borrow to it, this is not connected to printing.

3 
use std::str::CharIndices;

struct Parse {
    pos: usize,
    input: String,
}

impl Parse {
  fn new(source: String) -> Self {
    Self {
      pos: 0,
      input: source,
    }
  }

  fn parse_nodes(&mut self) -> usize {
    for _ in 0..self.next_ele().count() {
        self.pos += 1;
    }
    self.pos
  }
  fn next_ele(&self) -> CharIndices {
    self.input.char_indices()
  }
}

fn main() {
    let mut v = Parse::new("<div><div></div></div>".to_string());
    let c = v.parse_nodes();
    println!("{}",c);
}

Playground
But there is a little trick here.

4

Couldn't this be written to avoid the loop in the first place?

fn parse_nodes(&mut self) -> usize {
  self.pos += self.next_ele().count();
  self.pos
}
5

if there is no other work in the loop, you're right

6

I don't understand ,could you explain ?

7

Why are index and char involved here? This is what I mean when I talk about some extra work in the loop.

8

i got it .
index and char be invoked in other place,
there is a simplify code

1 Like
9

This topic was automatically closed 90 days after the last reply. We invite you to open a new topic if you have further questions or comments.