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. }

This slide should take about 5 minutes.

  • 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).