Move struct into a separate file without splitting into a separate module?

Question

I have this file hierarchy:

main.rs
protocol/
protocol/mod.rs
protocol/struct.rs

In struct.rs:

pub struct Struct {
    members: i8
}

impl Struct {
    pub fn new() -> Struct {
        Struct { 4 }
    }
}

How do I access it as:

mod protocol;
protocol::Struct::new();
// As opposed to:
// protocol::struct::Struct::new();

I've tried various combinations of pub use and mod but admittedly I'm poking at things blindly.

Is it possible to split a struct (and it's impl) into a separate file without having to create a new mod?

Answer 1

The short answer: use pub use Type in your mod.rs. A full example follows:

My structure:

src/
├── main.rs
├── protocol
│   └── thing.rs
└── protocol.rs

main.rs

mod protocol;

fn main() {
    let a = protocol::Thing::new();
    println!("Hello, {:?}", a);
}

protocol.rs

pub use self::thing::Thing;
mod thing;

protocol/thing.rs

#[derive(Debug)]
pub struct Thing(i8);

impl Thing {
    pub fn new() -> Thing { Thing(4) }
}

As a housekeeping bit, don't call files the same thing as language keywords. struct causes compilation problems, so I renamed it. Also, your struct creation syntax was incorrect, so I picked the shorter version for this example ^_^.

And to answer the question posed in your title: Without using esoteric features, a file always creates a new module — you can't put something into a different file without also putting it in a different module. You can re-export the type so it doesn't look like it though.

Further explanation: The mod keyword tells the compiler to look for a file by that name and reference it from the current file as a module. For example, mod protocol; will look for a file protocol.rs and behave as if it had included its contents, similar to:

mod protocol {
    // ... contents here
};

See Rust by Example for more details.

Answer 2

With mod.rs:

src/
├── main.rs
└── protocol
    ├── mod.rs
    └── thing.rs

protocol/thing.rs

pub struct Struct {
    members: i8
}

impl Struct {
    pub fn new() -> Struct {
        Struct { members: 4 }
    }
}

protocol/mod.rs

pub mod thing;

main.rs

mod protocol;

fn main() {
    protocol::thing::Struct::new();
}