Summary - Modules
- Rust course
- Intermediate
- Lesson 76/115
- 5 min
Combine mod, use and pub to set up a multi-file crate.
Modules summary
mod builds a module tree; items are private by default and opened with pub (struct fields individually). use shortens paths, as renames, pub use re-exports. Paths can start with crate::, super:: or self::. Modules can go in separate files (ag.rs, ag/istemci.rs). Fine-grained visibility: pub(crate), pub(super).
A private inner module
Library authors put details into private inner modules and expose a small surface:
mod kutuphane {
mod ic {
pub fn gizli_hesap(x: i32) -> i32 {
x * 3
}
}
pub fn hesapla(x: i32) -> i32 {
ic::gizli_hesap(x) + 1
}
}
// kutuphane::ic::gizli_hesap(4); // error: ic is private
println!("{}", kutuphane::hesapla(4)); // 13Practice Small surface
Write the kutuphane module above: gizli_hesap in the private ic module, and pub fn hesapla outside. Print the result of kutuphane::hesapla(4).
Starter code
fn main() {
// buraya yaz
}Sample solution
mod kutuphane {
mod ic {
pub fn gizli_hesap(x: i32) -> i32 {
x * 3
}
}
pub fn hesapla(x: i32) -> i32 {
ic::gizli_hesap(x) + 1
}
}
fn main() {
println!("{}", kutuphane::hesapla(4));
}Expected output
13
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 How do you fully hide an inner module and expose just one function?
- It isn't possible
- Leave the module non-pub and wrap it with a pub fn above, or pub use it Correct answer
- Make the module pub
- Use unsafe
Explanation: The pub items of a private module can only be used by code that can see that module; exposing them needs a door from the parent.
2 Crate-wide visibility
____(crate) fn yardimci() {}pub(crate) fn yardimci() {}Explanation: pub(crate) opens the item only within the same crate.
3 Group summary
| Term | Meaning |
|---|---|
mod x { } |
Module |
pub |
Exposes |
use a::b |
Shortcut |
pub use |
Re-export |