Controlling Visibility Within the Same File Using 'pub'
Controlling Visibility Within the Same File Using ‘pub’
The pub keyword makes the item public and visible outside its scope.
Privacy Rules
The following are two privacy rules when declaring modules:
- Rule No: 1
If an item is public it can be accessed from anywhere, i.e., within main function or any other module.
Example : Invoke a Public Function Directly
The following example declares a function public print_statement() within the mod r:
// declare a module
mod r {
pub fn print_statement(){
println!("Hi, this a function of module r");
}
}
// main function
fn main() {
println!("Let's go inside the module");
// invoke a module 'r'
r::print_statement();
}
output
Let's go inside the module
Hi, this a function of module r
Rule No: 2
If an item is private it can be accessed using its parent module meaning it can be accessed within the module but not outside it.
Example: Invoke a Private Function Indirectly through a Public Function
The example declares a module mod r which has two functions:
- A public function my_public_function()
- A private function my_private_function().
self can refer to a function or any item within the same module.
// declare a module
mod r{
fn my_private_function(){
println!("Hi, I'm a private function within the module");
}
pub fn my_public_function(){
//! also works without writing self i.e.
//! my_private_function();
println!("Hi,I'm a public function within the module");
println!("I'll invoke private function within the module");
self::my_private_function();
}
}
// main function
fn main() {
println!("Let's go inside the module");
// invoke a module 'r'
r::my_public_function();
}
output
Let's go inside the module
Hi,I'm a public function within the module
I'll invoke private function within the module
Hi, I'm a private function within the module
If an item is private, it can be called from within the child module.
Example: Access a Private Function through a Child Module
📝If there is a module within the module, then the outer module is called the parent module and the module inside the parent module is called the child module. This is known as a nested module
The example declares a module mod outer_module which has:
- A private functionmy_private_function().
inner_module- Inner module has one public functionmy_public_function()
The following example shows how the private function is accessed in the child module using the keyword super followed by
:: and the function name in the parent module.
super keyword refers to the parent module.
// main function
fn main() {
println!("Let's go inside the module");
outer_module::inner_module::my_public_function();
}
// declare a module
mod outer_module {
// function within outer module
fn my_private_function() {
println!("Hi, I got into the private function of outer module");
}
// declare a nested module
pub mod inner_module {
// function within nested module
pub fn my_public_function() {
println!("Hi, I got into the public function of inner module");
println!("I'll invoke private function of outer module");
super::my_private_function();
}
}
}
output
Let's go inside the module
Hi, I got into the public function of inner module
I'll invoke private function of outer module
Hi, I got into the private function of outer module
Even though the function my_private_function() is declared private, the main() function is able to invoke it
indirectly because the function it calls is public.
Example: Access a Root Function
The example below shows how the root function (a function that exists outside the module) can be accessed within
the function of a module. Write super:: followed by the root function name.
super can allow accessing a root function from within the module.
// main function
fn main() {
println!("Let's go inside the module");
my_module ::my_public_function();
}
fn my_function(){
println!("Hi, you came inside the root function using super");
}
// declare a module
mod my_module {
// function within outer module
pub fn my_public_function() {
println!("Invoke root function");
super::my_function();
}
}
output
Let's go inside the module
Invoke root function
Hi, you came inside the root function using super
Quiz
Last updated 25 Jan 2024, 05:11 +0530 .