Rust: struct with vector of references to another vector of the struct

Question

I defined two structs like these:

#[derive(Debug)]
struct Slices<'a> {
    intervals: &'a[u32]
}

#[derive(Debug)]
struct NumbersWithSlices<'a> {
    numbers: Vec<u32>,
    slices: Vec<Slices<'a>>
}

and I managed to write a main like this:

fn main() {
    let raw: Vec<u32> = vec![0,1,2,3,4,5,6,7,8,9];
    
    let mut sf = NumbersWithSlices {
        numbers: raw,
        slices: vec![]
    };
    
    sf.slices.push(Slices{intervals: &sf.numbers[0..1]});
    sf.slices.push(Slices{intervals: &sf.numbers[1..3]});
    
    println!("{:?}", sf.slices[1].intervals[0]);
}

which works as I expected.

Now I would like to implement a new function fro NumbersWithSlices which mimics what I did in main: I end up with

impl<'a> NumbersWithSlices<'a> {
    fn new(numbers: Vec<u32>) -> Self {

        let mut res = Self {
            numbers,
            slices: vec![]
        };
        
        let start_idx = 0; // for the moment
        let stop_idx = 1; // for the moment
        res.slices.push(Slices{intervals: &res.numbers[start_idx..stop_idx]});
        
        return res;
    }
}

This code gives me an compilation error

error[E0505]: cannot move out of `res` because it is borrowed
  --> src/main.rs:25:16
   |
13 | impl<'a> NumbersWithSlices<'a> {
   |      -- lifetime `'a` defined here
...
16 |         let mut res = Self {
   |             ------- binding `res` declared here
...
23 |         res.slices.push(Slices{intervals: &res.numbers[start_idx..stop_idx]});
   |                                            ----------- borrow of `res.numbers` occurs here
24 |         
25 |         return res;
   |                ^^^
   |                |
   |                move out of `res` occurs here
   |                returning this value requires that `res.numbers` is borrowed for `'a`

error[E0515]: cannot return value referencing local data `res.numbers`
  --> src/main.rs:25:16
   |
23 |         res.slices.push(Slices{intervals: &res.numbers[start_idx..stop_idx]});
   |                                            ----------- `res.numbers` is borrowed here
24 |         
25 |         return res;
   |                ^^^ returns a value referencing data owned by the current function

I think I'm able to understand the error, but I cannot find how to write the correct code to get the result I want, just as written in main function.

Rust: struct with vector of references to another vector of the struct

0 Answers0