RS.CLIPPY.RC_BUFFER

Shared ownership of a buffer type

This checker is a Clippy lint created by The Rust Project Contributors. The documentation shown here is a copy of the original documentation for: rc_buffer. Copyright ©2025 The Rust Team. All rights reserved.

What it does

Checks for Rc<T> and Arc<T> when T is a mutable buffer type such as String or Vec.

Why restrict this?

Expressions such as Rc<String> usually have no advantage over Rc<str>, since it is larger and involves an extra level of indirection, and doesn't implement Borrow<str>.

While mutating a buffer type would still be possible with Rc::get_mut(), it only works if there are no additional references yet, which usually defeats the purpose of enclosing it in a shared ownership type. Instead, additionally wrapping the inner type with an interior mutable container (such as RefCell or Mutex) would normally be used.

Known problems

This pattern can be desirable to avoid the overhead of a RefCell or Mutex for cases where mutation only happens before there are any additional references.

Example

fn foo(interned: Rc<String>) { ... }

Better:

fn foo(interned: Rc<str>) { ... }

Configuration

avoid-breaking-exported-api: Suppress lints whenever the suggested change would cause breakage for other crates.

(default: true)