Modules

Noir's module system follows the same convention as the newer version of Rust's module system.

Purpose of Modules

Modules are used to organize files. Without modules all of your code would need to live in a single file. In Noir, the compiler does not automatically scan all of your files to detect modules. This must be done explicitly by the developer.

Examples

Importing a module in the crate root

Filename : src/main.nr

mod foo;

fn main() {
    foo::hello_world();
}

Filename : src/foo.nr

fn from_foo() {}

In the above snippet, the crate root is the src/main.nr file. The compiler sees the module declaration mod foo which prompts it to look for a foo.nr file.

Visually this module hierarchy looks like the following :

crate
 ├── main
 │
 └── foo
      └── from_foo

The module filename may also be the name of the module as a directory with the contents in a file named mod.nr within that directory. The above example can alternatively be expressed like this:

Filename : src/main.nr

mod foo;

fn main() {
    foo::hello_world();
}

Filename : src/foo/mod.nr

fn from_foo() {}

Note that it's an error to have both files src/foo.nr and src/foo/mod.nr in the filesystem.

Importing a module throughout the tree

All modules are accessible from the crate:: namespace.

crate
 ├── bar
 ├── foo
 └── main

In the above snippet, if bar would like to use functions in foo, it can do so by use crate::foo::function_name.

Sub-modules

Filename : src/main.nr

mod foo;

fn main() {
    foo::from_foo();
}

Filename : src/foo.nr

mod bar;
fn from_foo() {}

Filename : src/foo/bar.nr

fn from_bar() {}

In the above snippet, we have added an extra module to the module tree; bar. bar is a submodule of foo hence we declare bar in foo.nr with mod bar. Since foo is not the crate root, the compiler looks for the file associated with the bar module in src/foo/bar.nr

Visually the module hierarchy looks as follows:

crate
 ├── main
 │
 └── foo
      ├── from_foo
      └── bar
           └── from_bar

Similar to importing a module in the crate root, modules can be placed in a mod.nr file, like this:

Filename : src/main.nr

mod foo;

fn main() {
    foo::from_foo();
}

Filename : src/foo/mod.nr

mod bar;
fn from_foo() {}

Filename : src/foo/bar/mod.nr

fn from_bar() {}

Referencing a parent module

Given a submodule, you can refer to its parent module using the super keyword.

Filename : src/main.nr

mod foo;

fn main() {
    foo::from_foo();
}

Filename : src/foo.nr

mod bar;

fn from_foo() {}

Filename : src/foo/bar.nr

// Same as bar::from_foo
use super::from_foo; 

fn from_bar() {
    from_foo();        // invokes super::from_foo(), which is bar::from_foo()
    super::from_foo(); // also invokes bar::from_foo()
}