RRust By Example
intermediateOwnership

Mutable Borrow

Use mutable references to modify borrowed data.

Mutable Borrow

Use mutable references to modify borrowed data.

Difficulty

Intermediate

Code

rust
fn push_world(s: &mut String) {
    s.push_str(", world!");
}

fn main() {
    let mut s = String::from("hello");
    push_world(&mut s);
    println!("{}", s);
}

Explanation

Mutable references (&mut) allow modification. Only one mutable reference at a time.

Key Concepts

  • Read the code carefully and understand the data flow
  • Try modifying the example to see how it changes behavior
  • Run this code in the Rust Playground

Related Topics

Browse more examples in the ownership category to build a complete understanding of this topic.

Common Compiler Errors in This Topic

Use these error pages as a debugging companion while practicing this example category.

E0382

use of moved value

Learn what Rust error E0382 means, why it happens, and how to fix it with practical code examples.

E0507

cannot move out of borrowed content

Learn what Rust error E0507 means, why it happens, and how to fix it with practical code examples.

E0499

cannot borrow more than once at a time

Learn what Rust error E0499 means, why it happens, and how to fix it with practical code examples.

E0597

borrowed value does not live long enough

Learn what Rust error E0597 means, why it happens, and how to fix it with practical code examples.

More Ownership Examples

Borrowing

Use references to borrow values without taking ownership.

Clone and Copy

Deep copy with Clone and stack copy with Copy trait.

Closure Ownership

How closures capture values: by reference, mutable reference, or by value.

Non-Lexical Lifetimes

Understanding how Rust determines borrow lifetimes.