Keyword in

Iterate over a series of values with for.

The expression immediately following in must implement the IntoIterator trait.

Literal Examples:

• for _ in 1..3 {} - Iterate over an exclusive range up to but excluding 3.
• for _ in 1..=3 {} - Iterate over an inclusive range up to and including 3.

(Read more about range patterns)

The other use of in is with the keyword pub. It allows users to declare an item as visible only within a given scope.

Literal Example:

• pub(in crate::outer_mod) fn outer_mod_visible_fn() {} - fn is visible in outer_mod

Starting with the 2018 edition, paths for pub(in path) must start with crate, self or super. The 2015 edition may also use paths starting with :: or modules from the crate root.

For more information, see the Reference.