Smart Pointers

A smart pointer is a data structure that acts like a pointer but also has additional metadata and capabilities. Smart pointers are a powerful feature in Oxide that give you more flexibility and safety than ordinary references.

In this chapter, we'll explore the most important smart pointers in Oxide's standard library:

• Box<T> - For allocating values on the heap
• Rc<T> - For multiple ownership via reference counting
• RefCell<T> - For interior mutability patterns
• Reference cycles - How to avoid memory leaks with circular references

What are Smart Pointers?

Smart pointers are pointers with additional behavior and metadata. The most common smart pointers in the standard library provide functionality beyond what references provide: they manage memory automatically through ownership and borrowing, just like Oxide's core reference system.

Smart pointers are typically implemented using structs, but they implement the Deref and Drop traits to give them pointer-like behavior:

• The Deref trait allows a smart pointer to be treated like a regular reference through deref coercion
• The Drop trait lets you customize what happens when a smart pointer goes out of scope

When to Use Smart Pointers

Smart pointers solve different problems:

• Box<T>: When you need to move a large value or allocate something on the heap
• Rc<T>: When you need multiple parts of your program to own the same data
• RefCell<T>: When you need interior mutability—the ability to mutate data even through an immutable reference

Let's explore each one in detail.

Comparing Smart Pointers

Here's a quick comparison of the three main smart pointers:

As you read through this chapter, you'll understand when and why to use each one.

A Note on Performance

The Oxide compiler optimizes smart pointer operations aggressively. In many cases, the overhead of smart pointers is eliminated through inlining and monomorphization. However, Rc<T> and RefCell<T> do have runtime costs because they maintain additional state, so use them thoughtfully in performance-critical code.

In the next section, we'll dive into Box<T>, the simplest and most commonly used smart pointer.