出口和可见度

目录结构：

yourproject/
    Cargo.lock
    Cargo.toml
    src/
        main.rs
        writer.rs

main.rs

// This is import from writer.rs
mod writer;

fn main() {
    // Call of imported write() function.
    writer::write()
    
    // BAD
    writer::open_file()
}

writer.rs

// This function WILL be exported.
pub fn write() {}

// This will NOT be exported.
fn open_file() {}