Box
Box is a Rust owning smart pointer that provides indirection by storing a uniquely owned value in heap-allocated memory.
Learn Rust in a Month of Lunches
Box is Rust's owning smart pointer that stores a value on the heap while keeping a fixed-size pointer on the stack.
- How it is used
- Uses an owning heap pointer to make recursive structs and trait-object returns possible when a value’s size cannot be known directly.
- How deep it goes
- Works through construction, dereferencing, recursive-type compiler feedback, trait objects, multiple errors, and downcasting; does not develop linked-list construction.
- Examples
- Shows a boxed integer, a recursive struct corrected after a compiler error, a boxed trait return, and functions returning multiple error types.
- What you can do after
- Apply it via Rust’s `Box::new` to construct recursive values or return `Box<dyn Error>`, then try downcasting when the concrete error matters.
Rust in Action: Systems programming concepts and techniques
Box is Rust's owning smart pointer type for storing a value on the heap while keeping a pointer to it in the containing value.
- How it is used
- Uses Box to place values on the heap and to return trait-object errors from operations with different error types.
- How deep it goes
- Explains allocation, stack pointers, dereferencing, explicit drop, and why boxed trait objects have a known stack size.
- Examples
- Works through boxed integer addition, allocation and drop of boxed numbers, and a boxed error return type.
- What you can do after
- Apply it via Rust's Box::new to allocate a value, dereference it, and use Box<dyn Error> for differing errors.
Read how Rust in Action: Systems programming concepts and techniques explains Box →
Code Like a Pro in Rust
Box is a Rust smart-pointer type that provides unique ownership of a value allocated on the heap.
- How it is used
- Allocates a single value on the heap, including values held in linked-list nodes.
- How deep it goes
- Explains allocation and deallocation, then implements boxed linked-list links; leaves allocation-failure handling outside the worked example.
- Examples
- Builds a singly linked list with boxed data and optional boxed successors, then traverses its items.
- What you can do after
- Build it from scratch: represent and traverse a singly linked list using Box and Option.
Idiomatic Rust
Box is a Rust standard-library owning pointer that stores a value on the heap and provides indirection.
- How it is used
- Uses Box for heap allocation without shared ownership and for placing unsized trait objects in sized containers.
- How deep it goes
- Explains pointer choice, trait-object coercion, and redundant nested allocation through focused code examples.
- Examples
- Demonstrates Vec<Box<dyn MyTrait>> for mixed implementations and contrasts Vec<Box<String>> with Vec<String>.
- What you can do after
- Apply Box to heap-allocate single-owner values, contain trait objects, and avoid unnecessary boxing inside Vec.
Related concepts
- smart pointerkind of · A smart pointer is a pointer-like object that manages or mediates access to a referenced resource, often providing ownership, lifetime, or safety behavior.
- trait objectused by · A Rust trait object is a value accessed through a trait interface with its concrete implementing type hidden and methods dispatched dynamically.
- referencekind of · A reference is an indirect value or relationship that identifies or provides access to another value, object, resource, or source.
- vectoralternative to · A vector is an ordered, indexed sequence of elements, often numerical, represented as a mathematical quantity or a computational collection.
- memory allocationuses · Memory allocation is the process of reserving or assigning storage for program data and objects during execution.
- recursive data structureaddresses · A recursive data structure is a structure whose definition directly or indirectly refers to another instance of the same structure.
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