Cow
Cow is Rust’s standard-library clone-on-write type, representing either borrowed or owned data and creating owned data when necessary.
Learn Rust in a Month of Lunches
Cow is a Rust standard-library clone-on-write enum that can represent either borrowed data or owned data and create an owned copy when necessary.
- How it is used
- Chooses between borrowed and owned values when a function or structure may need either representation.
- How deep it goes
- Explains variants, generics, lifetimes, ToOwned, dynamically sized types, matching, and conversion methods.
- Examples
- Uses conditional message generation and User names to contrast borrowed values with allocated owned values.
- What you can do after
- Apply it via std::borrow::Cow to accept, return, or store borrowed and owned data in one type.
Idiomatic Rust
Cow is Rust's standard-library copy-on-write smart pointer that can represent either borrowed data or owned data.
- How it is used
- Uses clone-on-write to preserve source data while allowing mutations to work on an owned value.
- How deep it goes
- Defines Borrowed and Owned variants, ToOwned bounds, Deref, and to_mut cloning without detailing implementation internals.
- Examples
- Demonstrates string replacement, a conditional loud_moo transformation, and a Cow-backed list that preserves earlier values.
- What you can do after
- Apply it via Rust’s standard library to mutate a Cow-backed value while leaving the source unchanged.
Related concepts
- copy-on-writeimplements · Copy-on-write is a technique that shares data until modification requires creating an independent copy, preserving the original for existing users.
- Derefimplements · Deref is a Rust standard-library trait that defines how a value is dereferenced to access a target value and enables dereference coercions.
- 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.
- enumkind of · An enum is a type or language construct whose values are selected from a finite set of named alternatives, which may carry associated data.
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