Ownership Rules

Rust's ownership model ensures memory safety without needing a garbage collector. Ownership rules are crucial for writing safe and efficient Rust code. Sometimes, beginners may write code that violates these rules. In this challenge, you will fix a piece of Rust code that has ownership rule violations.

Ownership Rules

Here are some important ownership rules to remember:

Each value in Rust has a variable that's called its owner.
There can only be one owner at a time.
When the owner goes out of scope, the value will be dropped.
You can have either one mutable reference or any number of immutable references, but not both simultaneously.

Your task

Before starting to solve the challenge, try to run the code and see what error you'll get. This will help you understand the problem better.

The compile error tells us that we can't borrow s as mutable because it is also borrowed as immutable. If we borrow it as mutable, the value will change and the compiler can not guarantee that the immutable reference hasn't changed.

You are given a function calculate_and_modify that violates Rust's ownership rules. Your task is to identify and fix the ownership rule violations in this function.

Fix the code to adhere to Rust's ownership rules.
The code should print the reference s2 after without any ownership rule violations.
The code should run the push_str method to mutate the string.
The code should return the modified string and its length.

Hints

You only need to change the order of the function calls, just make sure you don't have invalid references.

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Solutions

Esteban Soba

XtebanUy

an hour ago

5.00ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

woke-developer

an hour ago

5.18ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Markus Bergkvist

mbergkvist

an hour ago

5.46ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

facat

5 hours ago

6.61ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Jaden Wijata

xenonminer

8 hours ago

5.62ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    
    s.push_str(", world");
    (s, length)
}

Ando “Thor” Nando

DivineGod

15 hours ago

5.53ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Andreas

StimhackSoftware

16 hours ago

5.39ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

mehdihmr

18 hours ago

5.45ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Mister Woody

MisterWoody

19 hours ago

5.26ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Ethel Arterberry

ethel-dev

a day ago

5.91ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Algorab

a day ago

6.29ms

103.10kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Johannes Pfabe

Hannnsen

a day ago

6.68ms

103.10kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Stefan Roas

sroas

a day ago

12.07ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    s.push_str(", world");
    (s, length)
}

Felipe Balbi

felipebalbi

a day ago

5.94ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

xiuchiliudu

2 days ago

7.80ms

103.13kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &mut s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Daniel Petrov

danielmpetrov

2 days ago

5.84ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

chuyuanlinzi

2 days ago

9.20ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

yoakemae

2 days ago

5.42ms

103.67kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s2.to_string(), length)
}

Yossa Bourne

terminox

2 days ago

7.16ms

103.14kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

qiyuan711

3 days ago

7.78ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Jan Willems

3 days ago

6.45ms

103.61kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s.to_string(), length)
}

Jan Willems

3 days ago

10.23ms

103.67kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s2.to_string(), length)
}

Nicky Thorne

nickythorne

3 days ago

6.06ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Philip Mercer

DV-13

3 days ago

5.96ms

103.14kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

tinthid

3 days ago

6.05ms

103.18kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let mut s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

martin-unit

3 days ago

6.48ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

RonaldoArayadev

3 days ago

5.36ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    s.push_str(", world");
    (s, length)
}

vrzwflng

4 days ago

6.59ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Jörg Erdmenger

joeslow

4 days ago

5.51ms

103.10kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Elizabeth Doughty

Thymelizabeth

4 days ago

8.13ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

s.konishi

konishu

5 days ago

5.32ms

103.10kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Masayuki Sunahara

tamanishi

5 days ago

5.54ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

devarajang

5 days ago

6.55ms

103.65kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s2.clone(), length)
}

nichideropa

5 days ago

7.17ms

103.14kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;// immutable reference to s
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

akshayabhattarai

5 days ago

8.51ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Jan

jeypiti

5 days ago

6.07ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

stefafafan

5 days ago

5.41ms

103.03kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2);
    (s, length)
}

0xsmarter

6 days ago

5.12ms

102.89kb

pub fn calculate_and_modify() -> (String, usize) {
    let  s = String::from("hello");
    let length = s.len();
    let mut s2 = s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s2, length)
}

madeinheaven91

6 days ago

5.59ms

102.93kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let mut s2 = s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s2, length)
}

t3stlab

6 days ago

5.63ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

aidan1magee

6 days ago

5.43ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

tsuchiya-d

tsucchinoko

6 days ago

5.51ms

103.08kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Ankeet Parikh

ankeetparikh

7 days ago

5.25ms

103.10kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

koslowskio

7 days ago

5.16ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
   
    s.push_str(", world");
     let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

maxvi

7 days ago

6.04ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Lauri Sarap

LauriSarap

7 days ago

11.05ms

102.98kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &s;
    println!("{}", s2);
    
    s.push_str(", world");
    (s, length)
}

Rafael Lucas

rafaellucasprogm

8 days ago

5.28ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Rafael Lucas

rafaellucasprogm

8 days ago

5.21ms

103.09kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    s.push_str(", world");
    let s2 = &s;
    
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Rocky.C

cloki0610

8 days ago

5.43ms

103.14kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();
    let s2 = &mut s;
    s2.push_str(", world");
    println!("{}", s2); // uses an old reference that has been changed `s2`
    (s, length)
}

Tsubasa Shimomura

tsubasa-s

8 days ago

5.39ms

103.11kb

pub fn calculate_and_modify() -> (String, usize) {
    let mut s = String::from("hello");
    let length = s.len();    
    let s2 = &s;
    println!("{}", s2); // uses an old reference that has been changed `s2`    
    s.push_str(", world");
   
    (s, length)
}