如何在 Rust 的内部循环中正确移动所有权？

Question

Question 1: How to properly move ownership of the data, in an inner loop, so that once the final iteration gets done, the container iterated will be Drop() ed.

For example:

let left_strs: Vec<String> = Self::allowed(&slice[..i]);
let right_strs: Vec<String> = Self::allowed(&slice[i..]);
for left_str in left_strs{
    // how to properly move the ownership of the data here?
    for right_str in right_strs.iter(){
        ans.push(format!("({}, {})", left_str, right_str));
    }
}

Question 2: For all the data in the vector, its ownership has been moved, and it has been Drop() ed eventually, will the vector(container) be automatically Drop() ed because of this?

Answer 1

Easiest thing that comes to my mind is to use a new scope:

fn main() {
    let left_strs: Vec<String> = vec!["one".to_string(), "two".to_string()];
    {
        let right_strs: Vec<String> = vec!["one".to_string(), "two".to_string()];
        // use a & on left_strs to avoid move
        for left_str in &left_strs {            
            for right_str in right_strs.iter() {
                println!("({}, {})", left_str, right_str);
            }
        }
    // right_strs is drop
    }
    // we can still use left_strs, since we used a & before
    for s in left_strs {
        println!("{}", s);
    }
}

This way, right_strs will be drop when the scope ends.

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