As our crate grows and has more and more structs, enums, and functions, putting everything in the src/main.rs file will start to be confusing.

In order to better organize our code we might want to split it into multiple files. (and later maybe into multiple crates, but for now let's keep them in the same crate.

The functions

• It has one function called in_main and we can call it without any extra effort.

• In the src/lib.rs file we have function called in_lib.

  • It is declared with the pub keyword to make it public.

  • We can call it by prefixing the name with the name of the crate app::in_lib();. (app is the name of the crate as defined in the Cargo.toml file.)

• In the src/helper.rs file there is a function called in_helper. In order to make it usable in the main file:

  • We made it public with the pub prefix.
  • We also added pub mod helper; to the src/lib.rs file.
  • Now we can call it with its full name: app::helper::in_helper();

• Another function in the src/helper.rs called in_imported_helper.

  • We made it public with pub.
  • In src/lib.rs we added pub use helper::in_imported_helper; (imported it)
  • We can now call it app::in_imported_helper(); (without the exact location of the function.)

• In order to allow a a function in src/helper.rs to call a function in src/lib.rs

  • The function must be pub.

  • We prefix it with crate as in crate::in_lib().

Cargo.toml

examples/split-code/Cargo.toml

[package]
name = "app"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

The main.rs

examples/split-code/src/main.rs

use app::tools::in_tools;

fn main() {
    println!("in main function");
    in_main();
    app::in_lib();
    app::helper::in_helper();
    app::in_imported_helper();

    in_tools();
}


fn in_main() {
    println!("in src/main.rs");
}

lib.rs

examples/split-code/src/lib.rs

pub mod helper;
pub mod tools;

pub use helper::in_imported_helper;

pub fn in_lib() {
    println!("in_lib");
    helper::in_helper();
}

helper.rs

examples/split-code/src/helper.rs

pub fn in_helper() {
    println!("in_helper");
}

pub fn in_imported_helper() {
    println!("in_imported_helper");

    crate::in_lib()
}

tools.rs

examples/split-code/src/tools.rs

pub fn in_tools() {
    println!("in_tools");

    crate::helper::in_helper();
}