Chapter 19: Smart Pointers

Memory management is a critical aspect of systems programming. C programmers are accustomed to managing memory manually using raw pointers (*T) and functions like malloc() and free(). This approach offers fine-grained control but is notoriously prone to errors like memory leaks, double frees, and use-after-free bugs.

Rust takes a different approach. It strongly encourages stack allocation and employs compile-time-checked references (&T, &mut T) for borrowing data. These references ensure memory safety for many common patterns without requiring manual deallocation. However, certain scenarios require more explicit control over memory allocation, ownership strategies, and lifetime management, particularly when dealing with heap data or shared access. This is where Rust’s smart pointers come into play.

Smart pointers in Rust are typically structs that wrap some form of pointer (often a raw pointer internally) but provide enhanced behavior and guarantees. They own the data they point to and manage its lifecycle, most notably by automatically handling deallocation when the smart pointer goes out of scope (via the Drop trait). They integrate seamlessly with Rust’s ownership and borrowing rules, providing memory safety guarantees.

This chapter introduces the most common smart pointers in the Rust standard library, explores their use cases, and contrasts them with memory management techniques in C and C++. We will see how they help prevent the memory safety issues endemic to manual memory management while providing necessary flexibility.