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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In order to solve the challenge, please visit this page on a desktop computer.

Solutions

ogaca42

3 hours ago

4.73ms

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)
}

Shadawck

shadawck

4 hours ago

4.79ms

103.31kb

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

st01011

5 hours ago

4.59ms

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)
}

Maxence Potier

Mxn-ptr

5 hours ago

4.45ms

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)
}

ShileiShen

6 hours ago

4.57ms

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)
}

苏扬

suiang

6 hours ago

4.69ms

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)
}

jamtg

6 hours ago

5.04ms

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)
}

Daniel Yan

yansq

8 hours ago

4.50ms

103.10kb

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");
   
     // uses an old reference that has been changed `s2`
    (s, length)
}

oTTeuM

oTTeuMsTudio

8 hours ago

4.99ms

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)
}

ctylx

10 hours ago

4.32ms

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)
}

ctylx

10 hours ago

4.51ms

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)
}

Gear

macgeargear

11 hours ago

4.48ms

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)
}

funny_233

funny233-github

11 hours ago

4.51ms

103.26kb

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

zelsazgh

13 hours ago

4.67ms

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)
}

VladyslavY

16 hours ago

4.42ms

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)
}

José Bernardo

jose-bernardo

17 hours ago

4.36ms

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)
}

Tiago Silva

tiagombsilva

20 hours ago

5.24ms

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)
}

Delta Regeer

digitalresistor

20 hours ago

4.50ms

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)
}

Delta Regeer

digitalresistor

20 hours ago

4.43ms

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)
}

Carlos Arias

carlos-quantexai

21 hours ago

4.66ms

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)
}

Maki-SIO

a day ago

4.44ms

102.97kb

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)
}

Maki-SIO

a day ago

4.42ms

102.97kb

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)
}

Logan Radloff

radloffl

a day ago

4.42ms

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)
}

retinotopic

a day ago

4.76ms

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) 
}

今何求

jhq223

2 days ago

4.53ms

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)
}

Will Barnett

xbarnett

2 days ago

4.38ms

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)
}

Mikhail

mk-comm

2 days ago

4.39ms

103.09kb

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");
     // uses an old reference that has been changed `s2`
    (s, length)
}

Johnchoi913

2 days ago

4.43ms

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)
}

majesticalcreature

2 days ago

4.82ms

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)
}

Matei Stefanescu

matei

2 days ago

4.30ms

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)
}

sander-b-postnl

2 days ago

4.53ms

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)
}

Edoardo A. Morosanu

edoardo-morosanu

2 days ago

4.40ms

103.03kb

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

i5.650

i5-650

2 days ago

4.52ms

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)
}

amassare

2 days ago

4.51ms

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)
}

Oleksandr Romanov

alexromanov

2 days ago

4.95ms

103.24kb

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

Zava

zavakid

2 days ago

4.59ms

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)
}

Ryumin

RiskyRomero

2 days ago

4.68ms

103.11kb

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)
    // test
}

IdoPort

2 days ago

4.54ms

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)
}

Ustin

2 days ago

5.06ms

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)
}

Laurențiu STOLERIU

LaurentiuStoleriu

3 days ago

4.62ms

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)
}

至尊宝

shankun

3 days ago

4.78ms

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)
}

Parallaxes

3 days ago

4.63ms

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)
}

Dylan Park

dylan-park

3 days ago

4.59ms

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)
}

Xinoi

3 days ago

4.46ms

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)
}

Jonathan Lopez

otherJL0

3 days ago

4.72ms

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)
}

Stefano Cianciulli

CianciuStyles

3 days ago

4.51ms

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)
}

Ayush Rawat

ayushrawat10

3 days ago

4.32ms

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)
}

Patrik Bjärterot

pbjarterot

3 days ago

4.45ms

103.25kb

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

masteryachty

3 days ago

4.36ms

103.24kb

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

damascussteel21

3 days ago

4.59ms

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)
}