Mutable reference
A mutable reference is a reference or handle through which the referenced value or storage location may be modified, subject to language-specific access rules.
Learn Rust in a Month of Lunches
A mutable reference is a Rust reference that permits modification of its referent and must be the sole active reference to that referent.
- How it is used
- Uses mutable references to change values directly and through functions without transferring ownership.
- How deep it goes
- Works through `&mut`, dereferencing, reference rules, and compiler feedback, including when a mutable borrow ends after its last use.
- Examples
- Shows numeric updates, a shared-presentation analogy, a compiler borrow error and correction, and a function that appends to a string.
- What you can do after
- Build it from scratch with `&mut`, dereference it to update a value, and pass it to a function without moving ownership.
Read how Learn Rust in a Month of Lunches explains mutable reference →
Refactoring to Rust
A mutable reference is a Rust non-owning reference that permits modification of the referenced value under Rust's aliasing rules.
- How it is used
- Uses mutable references to update borrowed values while preserving ownership and making mutation visible in function signatures.
- How deep it goes
- Explains syntax, ownership-preserving borrowing, aliasing rules, and scope-based validity through an incremental artwork example.
- Examples
- Demonstrates repeated artwork viewing and an incrementing view counter implemented with borrowed references.
- What you can do after
- Apply mutable references to write functions that modify borrowed structs while respecting Rust’s exclusive-aliasing rules.
Code Like a Pro in Rust
A mutable reference is a reference through which the referenced value may be modified.
- How it is used
- Uses exclusive borrowing to modify existing data safely and support in-place operations.
- How deep it goes
- Explains borrow-checker exclusivity and signature-based copy detection, but defers detailed underlying algorithms.
- Examples
- Uses make_ascii_lowercase for in-place mutation and contrasts it with to_lowercase returning a copied String.
- What you can do after
- Apply &mut parameters to implement in-place mutation and diagnose likely copying from function signatures.
Read how Code Like a Pro in Rust explains mutable reference →
Related concepts
- referencecontrasts with · An immutable Rust reference is a non-owning borrow that provides read-only access to a value without taking ownership of it.
- immutable collectioncontrasts with · An immutable collection is a collection whose membership and contents cannot be changed after creation.
- self parametercontrasts with · A self parameter is a method receiver representing the instance or object on which the method operates or is invoked.
- referencekind of · A reference is an indirect value or relationship that identifies or provides access to another value, object, resource, or source.
- interior mutabilitycontrasts with · Interior mutability is a programming mechanism that permits mutation through an otherwise shared or immutable access path while enforcing safety through specialized checks or synchronization.
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