Control Visibility Within Different Files Using ‘pub’ link

When modules get large and become cumbersome to store in a single file, it is possible to move their definitions to a separate file to make the code easier to navigate. It is possible to access a module even if it belongs to a different file. To use the module in a different file, write mod followed by the name of the file in which the module is declared.

• Implicit Declaration A block of code put in a file without wrapping in a mod block implicitly declares a module.

• Import the module

  mod file_name
  

• Call the module

  file_name::x
  

Where x can be any construct within the module, i.e., function, array, trait, struct.

📝 Rust code is always put in files with .rs extension

Explicit Declaration link

The code in a file is wrapped within the mod block. This explicitly declares a module.

• Import the module

  mod file_name
  

• Call the module

      file_name::module_name::x
  

where x can be any construct within the module, i.e., function, array, trait, struct.

Privacy Rule link

• If the module belonging to some other file is to be made accessible then it should be made public by using the pub keyword before the mod.

📝Once the module is made public using pub, all privacy rules for defining modules within the same file apply.

Example link

The following example shows how a module in another file can be accessed.

• Implicit declaration The following example declares a module implicitly in a file my_mod.rs and calls it from main.rs. Note: In implicit declaration modules are public by default

main.rs

  mod my_mod; 

fn main() {

  println!("Invoke function in my_mod.rs");  

  my_mod::my_public_function();

}
  

my_mod.rs

  // declare a module
pub fn my_public_function() {
    println!("I am a public function in my_mod.rs");
}
  

output

  Invoke function in my_mod.rs
I am a public function in my_mod.rs
  

Explicit declaration link

• The following example declares a module module in a file my_mod.rs and call it from main.rs.

main.rs

  mod my_mod; 

fn main() {

  println!("I am a public function in my_mod.rs");

  my_mod::module::my_public_function();

}
  

my_mod.rs

  // declare a module
pub mod module{
pub fn my_public_function() {
    println!("I am a public function in my_mod.rs");
}
}
  

output

  I am a public function in my_mod.rs
I am a public function in my_mod.rs
  

Quiz link

Test your understanding of modules in different files.