Rust by Example

Visibility

By default, the items in a module have private visibility, but this can be overridden with the pub modifier. Only the public items of a module can be accessed from outside the module scope.

// A module named `my_mod`

mod my_mod {

// Items in modules default to private visibility.

fn private_function() {

println!("called `my_mod::private_function()`");

}

// Use the `pub` modifier to override default visibility.

pub fn function() {

println!("called `my_mod::function()`");

}

// Items can access other items in the same module,

// even when private.

pub fn indirect_access() {

print!("called `my_mod::indirect_access()`, that\n> ");

private_function();

}

// Modules can also be nested

pub mod nested {

pub fn function() {

println!("called `my_mod::nested::function()`");

}

#[allow(dead_code)]

fn private_function() {

println!("called `my_mod::nested::private_function()`");

}

// Functions declared using `pub(in path)` syntax are only visible

// within the given path. `path` must be a parent or ancestor module

pub(in crate::my_mod) fn public_function_in_my_mod() {

print!("called `my_mod::nested::public_function_in_my_mod()`, that\n> ");

public_function_in_nested();

}

// Functions declared using `pub(self)` syntax are only visible within

// the current module, which is the same as leaving them private

pub(self) fn public_function_in_nested() {

println!("called `my_mod::nested::public_function_in_nested()`");

}

// Functions declared using `pub(super)` syntax are only visible within

// the parent module

pub(super) fn public_function_in_super_mod() {

println!("called `my_mod::nested::public_function_in_super_mod()`");

}

}

pub fn call_public_function_in_my_mod() {

print!("called `my_mod::call_public_function_in_my_mod()`, that\n> ");

nested::public_function_in_my_mod();

print!("> ");

nested::public_function_in_super_mod();

}

// pub(crate) makes functions visible only within the current crate

pub(crate) fn public_function_in_crate() {

println!("called `my_mod::public_function_in_crate()`");

}

// Nested modules follow the same rules for visibility

mod private_nested {

#[allow(dead_code)]

pub fn function() {

println!("called `my_mod::private_nested::function()`");

}

// Private parent items will still restrict the visibility of a child item,

// even if it is declared as visible within a bigger scope.

#[allow(dead_code)]

pub(crate) fn restricted_function() {

println!("called `my_mod::private_nested::restricted_function()`");

}

}

}

fn function() {

println!("called `function()`");

}

fn main() {

// Modules allow disambiguation between items that have the same name.

function();

my_mod::function();

// Public items, including those inside nested modules, can be

// accessed from outside the parent module.

my_mod::indirect_access();

my_mod::nested::function();

my_mod::call_public_function_in_my_mod();

// pub(crate) items can be called from anywhere in the same crate

my_mod::public_function_in_crate();

// pub(in path) items can only be called from within the module specified

// Error! function `public_function_in_my_mod` is private

//my_mod::nested::public_function_in_my_mod();

// TODO ^ Try uncommenting this line

// Private items of a module cannot be directly accessed, even if

// nested in a public module:

// Error! `private_function` is private

//my_mod::private_function();

// TODO ^ Try uncommenting this line

// Error! `private_function` is private

//my_mod::nested::private_function();

// TODO ^ Try uncommenting this line

// Error! `private_nested` is a private module

//my_mod::private_nested::function();

// TODO ^ Try uncommenting this line

// Error! `private_nested` is a private module

//my_mod::private_nested::restricted_function();

// TODO ^ Try uncommenting this line

}

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