Visibility

Modules are a privacy boundary:

• Module items are private by default (hides implementation details).
• Parent and sibling items are always visible.
• In other words, if an item is visible in module foo, it’s visible in all the descendants of foo.

1. mod outer {
2. fn private() {
3. println!("outer::private");
4. }

6. pub fn public() {
7. println!("outer::public");
8. }

10. mod inner {
11. fn private() {
12. println!("outer::inner::private");
13. }

15. pub fn public() {
16. println!("outer::inner::public");
17. super::private();
18. }
19. }
20. }

22. fn main() {
23. outer::public();
24. }

• Use the pub keyword to make modules public.

Additionally, there are advanced pub(...) specifiers to restrict the scope of public visibility.

• See the Rust Reference).
• Configuring pub(crate) visibility is a common pattern.
• Less commonly, you can give visibility to a specific path.
• In any case, visibility must be granted to an ancestor module (and all of its descendants).