Day 2 - Memory doesn't grow on Christmas trees 🎄

Before we start

We'd like to clarify our intention behind Day 1 of Advent of Rust on Rustfinity. The challenge involved cloning a string to use it twice, which some people understandably judged too quickly and labeled as "teaching bad practice." We understand why it might have been seen this way, but that was not our goal.

The decision to use cloning was intentional, meant for educational purposes and to align with the story's style. We apologize for any misunderstanding this may have caused. In today's challenge, we'll revisit and demonstrate a better approach, showcasing more optimal Rust practices.

Thank you for your patience and understanding as the story continues to unfold!

Enjoy!

Santa stormed into the workshop like a grizzly bear that just got paged for an on-call issue at 3 AM. Santa's face twisted into a mix of frustration and disbelief—a dire sign that even his usually jolly demeanor couldn't mask the disappointment.

“Who wrote this monstrosity?!” Santa boomed, holding a printed stack of code like it was his naughty list. “Do you think memory grows on Christmas trees? CLONE?! Another allocation for the same string?!”

The room fell silent. The elves exchanged nervous glances; it seemed like the code you wrote yesterday wasn't up to Santa's standards.

“But Santa,” one of the elves began, “we thought cloning was safe! No borrow-checker drama—"

“Safe? Sure. Efficient? NO!” Santa interrupted. “We need to use references! Borrow the data, don’t hog it! Everything has its own place, and using .clone() here is not! This is Rust! Memory efficiency is the whole point!”

An elve raised a hand meekly. “But Santa, in JavaScript, you just put it in and it works!”

Santa sighed, pinching the bridge of his nose. “Listen, bros, here’s the deal: get this code refactored using references. If I see one more .clone() without a good reason, I’m switching to Zig. Now, fix it before I start yapping on stream about incompetent elves!”

The elves exchanged panicked glances, knowing that if they messed up, Blitzen would be called in to pair-program and nobody wanted that because Blitzen wouldn't stop talking about his neovim macros.

The elves gulped. It was time to work with something that they had never seen before: borrowing and references.

Can you help them fix the code?

Your task

Update the attach_message_to_present function to accept a reference to a String or a string slice str instead of an owned String.
Update the main function to pass a reference to the gift_message string instead of cloning it.

Editor not available on Mobile!

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

Solutions

Elena Sukmanova

sukman

34 minutes ago

360.47ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

rm-rf

admiraladmirable

an hour ago

356.73ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

M Bussonnier

Carreau

an hour ago

369.62ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Manta

Soecka

2 hours ago

394.37ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Tobias Vicenti

SchnobiTobi

2 hours ago

388.92ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Oliver Horn

ohorn

2 hours ago

364.83ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Stéphane Trebel

StephaneTrebel

2 hours ago

370.07ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Markus Wege

markuswege

3 hours ago

361.04ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Michel Casabianca

c4s4

3 hours ago

353.03ms

86.68kb

pub fn main() {
    let gift_message = "Merry Christmas! Enjoy your gift!";
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Michel Casabianca

c4s4

3 hours ago

355.19ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Alan Kleber

alankle

3 hours ago

349.61ms

88.42kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message.to_string());
}

Ruspoetin

3 hours ago

343.61ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Len Remmerswaal

LenRemmerswaal

3 hours ago

357.81ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

recursivemaze

3 hours ago

356.05ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

brunoalef7

3 hours ago

364.90ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

gkapkowski-saucelabs

4 hours ago

380.80ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

gkapkowski-saucelabs

4 hours ago

415.04ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

rawar089

6 hours ago

415.73ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Dasun Pubudumal

dasunpubudumal

6 hours ago

416.40ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

zealsham

7 hours ago

373.47ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

0x776a

midnightexigent

8 hours ago

380.45ms

86.68kb

pub fn main() {
    let gift_message = "Merry Christmas! Enjoy your gift!";
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Sergei Barbarash

sgt

8 hours ago

340.84ms

88.16kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", &gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Avi Avni

AviAvni

8 hours ago

420.94ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

var4yn

10 hours ago

339.93ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Hudson C. Dalprá

dalprahcd

10 hours ago

350.46ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

mrsalo

10 hours ago

382.14ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

WuHan0608

11 hours ago

367.10ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

neonwarp

11 hours ago

356.55ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Shun

aockgonnabefree

12 hours ago

672.59ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

LaserPH (Ethan)

LaserPH

14 hours ago

432.09ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

theandi667

15 hours ago

343.60ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Jeff Glaum

jeffglaum

16 hours ago

395.26ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

albert chang

0xkuznechik

17 hours ago

348.71ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Kj

kj-9

19 hours ago

340.80ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

jon-a-miller

19 hours ago

359.39ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

nikwi

20 hours ago

345.22ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Ryan Plauche

plauche

21 hours ago

346.58ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

David Pathakjee

dpathakj

a day ago

375.97ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Kada

Kada-quantum

a day ago

411.20ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Vabka

vabka

a day ago

345.03ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

jeremyp

jpekmez

a day ago

329.27ms

86.68kb

pub fn main() {
    let gift_message = "Merry Christmas! Enjoy your gift!";
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

IvanyaK

a day ago

411.53ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Maxime Biette

mbiette

a day ago

416.62ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Edgar Christian

edgarcnp

a day ago

345.70ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Matt Tuusberg

tuusberg

a day ago

415.73ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String ) {
    println!("The present now has this message: {}", message);
}

Yuankun Zhang

yuankunzhang

a day ago

356.83ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Li Feng

maplestarplayl

a day ago

388.40ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Rostyslav Bohomaz

rostyq

a day ago

437.85ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}

Grant Kinney

creativecoder

a day ago

425.78ms

88.11kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &String) {
    println!("The present now has this message: {}", message);
}

Filippo De Bortoli

filippodebortoli

a day ago

337.03ms

88.10kb

pub fn main() {
    let gift_message = String::from("Merry Christmas! Enjoy your gift!");
    attach_message_to_present(&gift_message);
    println!("{}", gift_message);
}
pub fn attach_message_to_present(message: &str) {
    println!("The present now has this message: {}", message);
}