Box pointer in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Box pointer in Rust?

A Box pointer is a smart pointer that stores data on the heap instead of the stack. It owns the data and cleans it up when it goes out of scope.

beginner

How do you create a Box pointer in Rust?

Use Box::new(value) to create a Box that owns value on the heap.

intermediate

Why use a Box pointer instead of a normal variable?

Because Box stores data on the heap, it can hold large or recursive data types without using stack space, and it allows for dynamic sized types.

beginner

What happens when a Box goes out of scope?

The Box automatically frees the heap memory it owns, preventing memory leaks.

beginner

How do you access the value inside a Box?

You can use the dereference operator * to get the value inside the Box.

What does Box::new(5) do in Rust?

A Creates a stack variable with value 5

B Creates a heap-allocated integer with value 5

C Creates a reference to an integer 5

D Creates a mutable integer 5

Box::new(5) allocates the integer 5 on the heap and returns a Box pointer owning it.

Which of these is true about Box pointers?

A They cannot be dereferenced

B They store data on the stack

C They automatically free heap memory when dropped

D They are used to borrow data temporarily

Box pointers own heap data and free it automatically when they go out of scope.

How do you get the value inside a Box named b?

A *b

B b.get()

C b.value()

D &b

Using *b dereferences the Box to access the owned value.

Why might you use a Box for recursive data types?

A To store data on the stack

B To borrow data temporarily

C To make data mutable

D To avoid infinite size at compile time

Recursive types need indirection like Box to have a known size at compile time.

What happens if you clone a Box?

A It clones the data on the heap

B It causes a compile error

C It creates a reference to the same data

D It copies the pointer but not the data

Cloning a Box clones the data it owns on the heap, creating a new heap allocation.

Explain what a Box pointer is and why it is useful in Rust.

Think about where data is stored and how Rust manages memory.

Describe how to create, use, and access data inside a Box pointer.

Consider how you put data in a box and get it back out.