Can't understand Rust module system

Question

I created a simple project for educational purpose, so I have a main function and 3 traits Battery, Display and GSM and implementations for them. I want the the main function to be in file main.rs and the 3 traits in another file called phone.rs:

phone.rs

mod phone{
    pub struct Battery{
        model : String,
        hours_idle : i16,
        hours_talk : i16
    }

    pub struct Display{
        size : i16,
        number_of_colors : i32
    }

    pub struct GSM{
        model : String,
        manufactor : String,
        price : f32,
        owner : String,
        battery: Battery,
        display : Display
    }

     impl Battery {
        pub fn new(model : String, hours_idle : i16, hours_talk : i16) -> Battery{
            Battery {model : model, hours_idle : hours_idle ,hours_talk : hours_talk}
        }
        pub fn print(&self){
            println!("Battery model: {}", self.model);
            println!("Hours idle: {}", self.hours_idle);
            println!("hours talk: {}", self.hours_talk);
        }
    }

    impl Display {
        pub fn new(size: i16, number_of_colors : i32) -> Display{
            Display{size : size, number_of_colors : number_of_colors}
        }
        pub fn print(&self){
            println!("size: {}", self.size);
            println!("number_of_colors: {}", self.number_of_colors);
        }
    }

     impl GSM {
        pub fn new(model : String, manufactor : String, price : f32, owner : String, battery : Battery, display : Display) -> GSM{
            GSM{model : model, manufactor : manufactor, price : price, owner : owner, battery : battery, display : display }
        }
        pub fn print(&self){
            println!("Model: {}, Manufactor: {}", self.model, self.manufactor);
            println!("price: {}", self.price);
            println!("owner: {}", self.owner);
            self.battery.print();
            self.display.print();
        }
    }
}

main.rs

pub mod phone;
fn main(){
    let battey = phone::Battery::new("modelBattery".to_string(), 1,2);
    let display =  phone::Display::new(10,20);
    //model : String, manufactor : String, price : f32, owner : String, baterry : Battery, display : Display
    let gsm =  phone::GSM::new("modelPhone".to_string(), "manufactor".to_string(), 100.0, "owner".to_string(), battey, display);
    gsm.print();
}

At first, everything was in one file (main.rs) and everything worked fine (there was some difference for example I added phone:: in front of Display, GSM and Battery in main.rs), when I moved the traits and added mod phone{} in phone.rs, and pub mod phone in main.rs, I got the following errors from the compiler:

src\main.rs:3:18: 3:37 error: failed to resolve. Could not find `Battery` in `phone` [E0433]
src\main.rs:3     let battey = phone::Battery::new("modelBattery".to_string(), 1,2);
                               ^~~~~~~~~~~~~~~~~~~
src\main.rs:3:18: 3:37 help: run `rustc --explain E0433` to see a detailed explanation
src\main.rs:3:18: 3:37 error: unresolved name `phone::Battery::new` [E0425]
src\main.rs:3     let battey = phone::Battery::new("modelBattery".to_string(), 1,2);
                               ^~~~~~~~~~~~~~~~~~~
src\main.rs:3:18: 3:37 help: run `rustc --explain E0425` to see a detailed explanation
src\main.rs:4:20: 4:39 error: failed to resolve. Could not find `Display` in `phone` [E0433]
src\main.rs:4     let display =  phone::Display::new(10,20);
                                 ^~~~~~~~~~~~~~~~~~~
src\main.rs:4:20: 4:39 help: run `rustc --explain E0433` to see a detailed explanation
src\main.rs:4:20: 4:39 error: unresolved name `phone::Display::new` [E0425]
src\main.rs:4     let display =  phone::Display::new(10,20);
                                 ^~~~~~~~~~~~~~~~~~~
src\main.rs:4:20: 4:39 help: run `rustc --explain E0425` to see a detailed explanation
src\main.rs:6:16: 6:31 error: failed to resolve. Could not find `GSM` in `phone` [E0433]
src\main.rs:6     let gsm =  phone::GSM::new("modelPhone".to_string(), "manufactor".to_string(), 100.0, "owner".to_string(), battey, display);
                             ^~~~~~~~~~~~~~~
src\main.rs:6:16: 6:31 help: run `rustc --explain E0433` to see a detailed explanation
src\main.rs:6:16: 6:31 error: unresolved name `phone::GSM::new` [E0425]
src\main.rs:6     let gsm =  phone::GSM::new("modelPhone".to_string(), "manufactor".to_string(), 100.0, "owner".to_string(), battey, display);
                             ^~~~~~~~~~~~~~~
src\main.rs:6:16: 6:31 help: run `rustc --explain E0425` to see a detailed explanation
src\main.rs:7:5: 7:16 error: the type of this value must be known in this context
src\main.rs:7     gsm.print();

I don't understand them, I searched here and in Google, but I failed to find a solution. Also I get a lot of warning that the methods in phone.rs are never used #[warn(dead_code)], any help is appreciated.

Rafaellle

Battery isn't a trait, it's a struct. – Binocular

Answer 1

Short answer: you don't need the mod phone in phone.rs. Just remove that and your code will work (assuming the rest of the code is correct).

Longer answer: The following code in main.rs:

pub mod phone;

is equivalent to:

pub mod phone {
    // literally insert the contents of phone.rs here
}

so you don't need to wrap everything in phone.rs in mod phone {}.

Your current code translates to:

pub mod phone {
    pub mod phone {
        pub struct Battery { ... }
        ...
    }
}

which means you need to access Battery as phone::phone::Battery (and Display as phone::phone::Display, etc.) in main.rs.

Ulcerate

Thank you, everything is working, I will give you "best answer" when I can. – Rafaellle

Answer 2

As you have written below in main.rs

pub mod phone;

Rust module system will start looking for a file named phone.rs at the directory level same as main.rs. And will include the code from phone.rs in main.rs. Since phone.rs code is wrapped under

mod phone{...}

So need be accessed like phone::phone::GSM. In order to prevent that just remove mod phone{}from phone.rs and bring the structs at top level and it should work with phone::GSM

Penury