mod aa;

fn main() {
    println!("------------------------------------");
    aa::aa1();

}

pub fn aa1(){
    println!("---aa-----");
}

$ cargo run
   Compiling crate_path v0.1.0 (/opt/wks/rust_study/crate_path)
    Finished dev [unoptimized + debuginfo] target(s) in 0.20s
     Running `target/debug/crate_path`
------------------------------------
---aa-----

mod aa;


fn main() {
    println!("------------------------------------------------");
    aa::bb::bb1();
    aa::cc::cc1();
}

pub mod bb;
pub mod cc;

pub fn bb1(){
    println!("-----------bb1-----------");
}

pub fn cc1(){
    println!("--------------cc1------------");
}

$ cargo new my-project
     Created binary (application) `my-project` package
$ ls my-project
Cargo.toml
src
$ ls my-project/src
main.rs

mod front_of_house {
    mod hosting {
        fn add_to_waitlist() {}

        fn seat_at_table() {}
    }

    mod serving {
        fn take_order() {}

        fn serve_order() {}

        fn take_payment() {}
    }
}

fn main() {}

crate
 └── front_of_house
     ├── hosting
     │   ├── add_to_waitlist
     │   └── seat_at_table
     └── serving
         ├── take_order
         ├── serve_order
         └── take_payment

A path can take two forms:

An absolute path starts from a crate root by using a crate name or a literal crate.
A relative path starts from the current module and uses self, super, or an identifier in the current module.
Both absolute and relative paths are followed by one or more identifiers separated by double colons (::).

mod bb {
    pub mod bb1{

        pub fn bb1_1(){
            println!("aa --> bb --> bb1 --> bb1_1");
        }

        pub fn bb1_2(){
            println!("-----self ----------------");
            self::bb1_1();
        }
    }

    pub fn bb2(){
        println!("aa --> bb --> bb2");
    }

    

}

//相当于在本crate中提供一个pub方法，供外部调用
use self::bb::bb1::bb1_1 as b1;
pub fn aa1(){
    b1();
}

//让pub bb2在其父mod bb私有的提前下，可供外部程序调用
//bb2本身必须pub 
pub use self::bb::bb2;

//对外提供一个pub模块
pub mod cc {

    //crate是绝对路径，root crate是main.rs
    use crate::aa::bb::bb1::bb1_2 as b2;
    pub fn cc1(){
        b2();
    }

    pub mod cc2{
        pub fn cc2_1(){
            println!("aa --> cc --> cc2 --> cc2_1");
        }
    }

}

mod aa;

use aa::cc::cc2;

fn main(){
    println!("-----------------------------------");
    aa::aa1();
    aa::cc::cc1();
    aa::bb2();
    cc2::cc2_1();
}

$ cargo run
   Compiling test_lib v0.1.0 (/opt/wks/rust_study/test_lib)
    Finished dev [unoptimized + debuginfo] target(s) in 0.21s
     Running `target/debug/test_lib`
-----------------------------------
aa --> bb --> bb1 --> bb1_1
-----self ----------------
aa --> bb --> bb1 --> bb1_1
aa --> bb --> bb2
aa --> cc --> cc2 --> cc2_1