---
title: "Chapter 9: References and Borrowing"
description: "The 8 lessons of chapter 9: References and Borrowing, in teaching order."
url: "https://learnrust.net/chapter-9/"
last_updated: "2026-06-12"
---

# Chapter 9: References and Borrowing

- [9.1 References: borrowing a value](https://learnrust.net/chapter-9/references-borrowing-a-value.md): Rust references let functions use a value without taking ownership: the & operator, borrowing, and why references are immutable by default.
- [9.2 Mutable references](https://learnrust.net/chapter-9/mutable-references.md): The &mut reference lets a function modify a borrowed value, under Rust's one-writer-or-many-readers rule, enforced by the borrow checker.
- [9.3 The borrow checker is your friend](https://learnrust.net/chapter-9/the-borrow-checker-is-your-friend.md): The four borrow checker errors every new Rust programmer hits in week one: E0596, E0502, E0382, and E0506, each read line by line and fixed.
- [9.4 References and functions](https://learnrust.net/chapter-9/references-and-functions.md): How to choose function parameter types in Rust: by value for Copy types, &T to read, &mut T to modify in place, and owned types to keep.
- [9.5 Dangling references](https://learnrust.net/chapter-9/dangling-references.md): What dangling references are, how C++ lets them happen, and how Rust's compiler refuses to let a reference outlive the value it points to.
- [9.6 Slices](https://learnrust.net/chapter-9/slices.md): Rust slices explained: borrowing a view of part of a sequence with range syntax, the &[T] type, and why functions take slices instead of arrays.
- [9.7 String slices](https://learnrust.net/chapter-9/string-slices.md): &str fully explained at last: string slices, range syntax on text, why parameters take &str over &String, and deref coercion.
- [9.x Chapter 9 summary and quiz](https://learnrust.net/chapter-9/chapter-9-summary-and-quiz.md): Review of references, borrowing, the borrow checker, dangling references, and slices, with a chapter quiz and a capstone program.

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