How to split the code in modules in Rust? [duplicate] - module

Question

This question already has an answer here:
Can't understand Rust module system
(1 answer)
Closed 3 years ago.
I am reading the Rust Book, I am in the chapter 7.2, but I must be missing something, because I cannot organize my code in modules, the compiler (rustc 1.32.0) keeps giving me errors.
What I have read
I read rustc --explain E0433, which is the advice of the compiler, but I still cannot solve it.
I checked Rust by examples, and it seems that my code is correct, (my/mod.rs is using module my/nested.rs in its own folder)
I found some info on Internet, but it is of 4 years ago, and include the use of use, which is not yet in the book.
I also checked this question, but I am not using folders, and again, it gets away from the book explanation.
Minimal example
This is a minimal example that tries to mimic the "sound" example of the book, there is only two files: /src/main.rs and /src/m.rs.
main.rs
mod m;
fn main() {
let st_0 = m::St::new();
}
m.rs
pub mod m {
pub struct St {
a:i32,
b:i32,
}
impl St {
pub fn new() -> St{
println!("New St!");
St {
a: 12,
b: 13,
}
}
}
}
And this is what cargo tells me:
Compiling min v0.1.0 (/home/user/min)
error[E0433]: failed to resolve: could not find `St` in `m`
--> src/main.rs:3:19
|
3 | let st_0 = m::St::new();
| ^^ could not find `St` in `m`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0433`.
error: Could not compile `min`.
To learn more, run the command again with --verbose.

Answer 1

When you have everything in one file, like this:
main.rs
pub mod m {
pub struct St {
a:i32,
b:i32,
}
impl St {
pub fn new() -> St{
println!("New St!");
St {
a: 12,
b: 13,
}
}
}
}
mod m;
fn main() {
let st_0 = m::St::new();
}
you wrap the module with the
pub mod mode_name {
//code...
}
Once you put the module in another file, that wrapping goes away. The Rust book, shows it, but if you don't look carefully or if you are programming drunk, you may get confused with the pub mod instrument {...} of the nested module.
So m.rs has to look like this:
pub struct St {
a:i32,
b:i32,
}
impl St {
pub fn new() -> St{
println!("New St!");
St {
a: 12,
b: 13,
}
}
}