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Answer: A crate is the smallest amount of code the Rust compiler considers at a time. Every package needs at least one crate (library, binary, or both).

Modules and privacy

Modules control item privacy; code inside a module stays private by default. Items in a parent module can't use the private items inside child modules.

Rust by Example calls a crate a compilation unit.

Claims

• id: C1 claim: A crate is the smallest amount of code the compiler considers at a time. source: S1 evidence: "A crate is the smallest amount of code that the Rust compiler considers at a"
• id: C2 claim: A package must contain at least one crate. source: S1 evidence: "A package must contain at least one crate, whether that's a library or binary crate."
• id: C3 claim: Modules control privacy because code within a module is private by default. source: S2 evidence: "Modules also allow us to control the privacy of items because code within a module"
• id: C4 claim: Parent modules cannot use private items inside child modules. source: S3 evidence: "Items in a parent module can't use the private items inside child modules, but items"

• id: C5 claim: A crate is a compilation unit in Rust. source: S4 evidence: "A crate is a compilation unit in Rust."

Sources

• [S1] Packages and Crates. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch07-01-packages-and-crates.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.
• [S2] Defining Modules to Control Scope and Privacy. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.
• [S3] Paths for Referring to an Item in the Module Tree. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.

• [S4] Crates - Rust By Example. Rust by Example (rust-lang/rust-by-example). https://doc.rust-lang.org/rust-by-example/crates.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_z61ytaw1,
  author = {{iinventedlight}},
  title = {{Rust packages, crates, and modules with privacy}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-09},
  url = {https://iinventedlight.com/library/notes/rust-packages-crates-modules/},
  note = {Permanent ID iil:note:z61ytaw1. License: CC-BY-4.0.},
}

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