}
// 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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Structs have an extra level of visibility with their fields. The visibility defaults to private, and can be overridden with the pub modifier. This visibility only matters when a struct is accessed from outside the module where it is defined, and has the goal of hiding information (encapsulation).
mod my {
// A public struct with a public field of generic type `T`
pub struct OpenBox<T> {
pub contents: T,
}
// A public struct with a private field of generic type `T`
#[allow(dead_code)]
pub struct ClosedBox<T> {
contents: T,
}
impl<T> ClosedBox<T> {
// A public constructor method
pub fn new(contents: T) -> ClosedBox<T> {
ClosedBox {
contents: contents,
}
}
}
}
fn main() {
// Public structs with public fields can be constructed as usual
let open_box = my::OpenBox { contents: "public information" };
// and their fields can be normally accessed.
println!("The open box contains: {}", open_box.contents);
// Public structs with private fields cannot be constructed using field names.
// Error! `ClosedBox` has private fields
//let closed_box = my::ClosedBox { contents: "classified information" };
// TODO ^ Try uncommenting this line
// However, structs with private fields can be created using
// public constructors
let _closed_box = my::ClosedBox::new("classified information");
// and the private fields of a public struct cannot be accessed.