Example
Let's see how we can organize the code, when the codebase is getting larger.
01. Functions
fn main() {
greet();
}
fn greet() {
println!("Hello, world!");
}
02. Modules - In the same file
fn main() {
greet::hello();
}
mod greet {
// By default, everything inside a module is private
pub fn hello() { // So function has to be public to access from outside
println!("Hello, world!");
}
}
03. Modules - In a different file in the same directory
When move some code to a new file, no need to wrap the code in a mod declaration. File itself acts as a module.
// ↳ main.rs
mod greet; // import greet module
fn main() {
greet::hello();
}
// ↳ greet.rs
pub fn hello() { // function has to be public to access from outside
println!("Hello, world!");
}
When move some code to a new file, if that code has been wrapped from a
moddeclaration, that will be a sub module of the file.
// ↳ main.rs
mod greet;
fn main() {
greet::hello::greet();
}
// ↳ greet.rs
pub mod hello { // module has to be public to access from outside
pub fn greet() { // function has to be public to access from outside
println!("Hello, world!");
}
}
04. Modules - In a different file in a different directory
When move some code to a new file in a different directory, directory itself acts as a module. And mod.rs in the module root is the entry point to the directory module. All other files in that directory, acts as a sub module of that directory.
// ↳ main.rs
mod greet;
fn main() {
greet::hello();
}
// ↳ greet/mod.rs
pub fn hello() {
println!("Hello, world!");
}
When you have multiple files in the module root,
// ↳ main.rs
mod greet;
fn main() {
greet::hello_greet()
}
// ↳ greet/mod.rs
mod hello;
pub fn hello_greet() {
hello::greet()
}
// ↳ greet/hello.rs
pub fn greet() {
println!("Hello, world!");
}
05. Modules - With self
fn main() {
greet::call_hello();
}
mod greet {
pub fn call_hello() {
self::hello();
}
fn hello() {
println!("Hello, world!");
}
}
06. Modules - With super
- When you want to access a root function from inside a module,
fn main() {
dash::call_hello();
}
fn hello() {
println!("Hello, world!");
}
mod dash {
pub fn call_hello() {
super::hello();
}
}
- When you want to access a function in outer/ parent module from inside a nested module,
fn main() {
outer::inner::call_hello();
}
mod outer {
pub fn hello() {
println!("Hello, world!");
}
mod inner {
pub fn call_hello() {
super::hello();
}
}
}
07. Modules - With use
- When you want to bind the full path to a new name,
use greet::hello::greet as greet_hello;
fn main() {
greet_hello();
}
mod greet {
pub mod hello {
pub fn greet() {
println!("Hello, world!");
}
}
}
- When you want to use crate scope level content
fn main() {
user::hello();
}
mod greet {
pub mod hello {
pub fn greet() {
println!("Hello, world!");
}
}
}
mod user {
use greet::hello::greet as call_hello;
pub fn hello() {
call_hello();
}
}
