Rust for C-Programmers

19.2 Smart Pointers vs. References

Understanding the distinction between references and smart pointers helps clarify when to use each:

References (&T and &mut T):

• Provide borrowed (non-owning) access to data.
• Never allocate or free memory.
• Are enforced at compile time so that a reference cannot outlive the data it points to.

Smart Pointers:

• Own their data and free it when they drop out of scope.
• Often incorporate special behavior (e.g., reference counting or runtime borrow checks).
• Integrate with Rust’s ownership and borrowing, catching many errors at compile time and sometimes at runtime (in the case of interior mutability).
• Are typically unnecessary for simple cases, but essential when you need shared ownership, heap allocation of custom structures, or interior mutability.

In essence, references represent ephemeral “borrows”, whereas smart pointers are full-blown owners that coordinate the lifecycle of their data. Both eliminate most of the problems associated with raw pointers in lower-level languages.