CODEWITHSUNDEEP
rustdeque
user4776812
user4776812

Reputation:

How to update value in VecDeque?

I want to store value in a VecDeque and after it updates the value:

use std::collections::VecDeque;

fn main() {
    let mut v = VecDeque::new();
    let mut str1 = String::from("Hello");
    
    v.push_back(str1);
    
    let str = String::from(" World");
    str1.push_str(&str);
}

   Compiling playground v0.0.1 (/playground)
error[E0382]: borrow of moved value: `str1`
  --> src/main.rs:10:5
   |
5  |     let mut str1 = String::from("Hello");
   |         -------- move occurs because `str1` has type `std::string::String`, which does not implement the `Copy` trait
6  |     
7  |     v.push_back(str1);
   |                 ---- value moved here
...
10 |     str1.push_str(&str);
   |     ^^^^ value borrowed here after move

How can I add item to collection and after it update this item?

Upvotes: 3

Views: 450

Answers (2)

user4776812
user4776812

Reputation:

My working example:

use std::collections::VecDeque;

fn main() {
    let mut v = VecDeque::new();
    let mut str1 = String::from("Hello");
    v.push_back(str1);

    let mut str2 = String::from(" World");

    match v.back_mut() {
        Some(value) => value.push_str(&str2),
        None => println!("Error")
    }

    match v.back() {
        Some(value) => println!("{}", value),
        None => println!("Error2")
    }
}

Upvotes: 3

limon
limon

Reputation: 917

Use back_mut

v.back_mut().unwrap().push_str(&str);

or just store reference in the deque

v.push_back(&mut str1);

Upvotes: 4

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