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Answer: Rc means reference counting: Rc<T> tracks how many handles point at a value. Some structures need multiple owners for one value.

Interior mutability

RefCell<T> checks borrow rules at runtime. Interior mutability lets you mutate data behind what looks like an immutable reference.

Rc supports multiple ownership by counting references.

Claims

• id: C1 claim: Rc keeps track of references via reference counting. source: S1 evidence: "abbreviation for reference counting. The Rc<T> type keeps track of the number of references to"
• id: C2 claim: In some cases a single value might have multiple owners. source: S1 evidence: "multiple owners. For example, in graph data structures, multiple edges might point to the same"
• id: C3 claim: With RefCell, borrowing invariants are enforced at runtime. source: S2 evidence: "With RefCell<T>, these invariants are enforced at runtime."
• id: C4 claim: Interior mutability allows mutating data behind immutable references. source: S2 evidence: "Interior mutability is a design pattern in Rust that allows you to mutate data even"

• id: C5 claim: When multiple ownership is needed, Rc (Reference Counting) can be used. source: S3 evidence: "When multiple ownership is needed, Rc(Reference Counting) can be used."

Sources

• [S1] Rc<T>, the Reference Counted Smart Pointer. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch15-04-rc.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.
• [S2] RefCell<T> and Interior Mutability Pattern. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch15-05-interior-mutability.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.

• [S3] Rc - Rust By Example. Rust by Example (rust-lang/rust-by-example). https://doc.rust-lang.org/rust-by-example/std/rc.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Sources and notices: The Rust Programming Language book (rust-lang/book): Copyright (c) 2010 The Rust Project Developers; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/book/blob/main/LICENSE-MIT). Rust by Example (rust-lang/rust-by-example): Copyright (c) 2014 Jorge Aparicio; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/rust-by-example/blob/master/LICENSE-MIT). Text was condensed and changed from the originals.

@misc{iil_note_69q9jwwr,
  author = {{iinventedlight}},
  title = {{Rc and RefCell interior mutability}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-09},
  url = {https://iinventedlight.com/library/notes/rust-rc-refcell/},
  note = {Permanent ID iil:note:69q9jwwr. License: CC-BY-4.0.},
}

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