Visibility & Privacy

Items are private by default. pub exposes across crates; restricted forms limit scope.

Recipe

pub struct Api {
    pub version: u32,
    secret: String,
}
 
impl Api {
    pub fn new(secret: String) -> Self {
        Self { version: 1, secret }
    }
}

When to reach for this: Encapsulating invariants - fields private, constructors controlled.

Working Example

mod internal {
    pub(crate) fn helper() {}
    pub(super) fn parent_only() {}
}
 
pub fn public_api() {
    internal::helper();
}

What this demonstrates:

• pub(crate) visible entire crate
• pub(super) parent module only
• Private by default inside module

Deep Dive

pub(in path) custom path visibility (Rust 2018+). Struct private fields with public type ok if in same crate patterns differ for consumers.

Gotchas

• pub struct private fields - External crate cannot construct without pub fn. Fix: Constructor.
• pub use reexport confusion - Hides actual path. Fix: Document prelude.
• Too pub - Leaks internals. Fix: pub(crate) default internal APIs.
• Test modules need pub - Or #[cfg(test)] in same module.
• macro exported privacy - #[macro_export] is public crate root.

Alternatives

FAQs

Related

• Modules Basics
• Designing a Public API
• Structs & Enums Best Practices
• use & Paths

External Related Links

• The Rust Reference - Formal language reference.
• The Rust Programming Language (The Book) - Canonical beginner-to-intermediate guide.
• Standard Library (std) Docs - Complete API reference for the standard library.
• Rust for Rustaceans (No Starch) - No Starch Press.
• Programming Rust: Fast, Safe Systems Development (Amazon) - Blandy, Orendorff, Tindall.

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.

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