use, super, self

A module can bring symbols from another module into scope with use. You will typically see something like this at the top of each module:

use std::collections::HashSet;
use std::process::abort;

Paths

Paths are resolved as follows:

  1. As a relative path:

    • foo or self::foo refers to foo in the current module,
    • super::foo refers to foo in the parent module.

  2. As an absolute path:

    • crate::foo refers to foo in the root of the current crate,
    • bar::foo refers to foo in the bar crate.
This slide should take about 8 minutes.

  • It is common to “re-export” symbols at a shorter path. For example, the top-level lib.rs in a crate might have

    mod storage;

pub use storage::disk::DiskStorage;
pub use storage::network::NetworkStorage;

    making DiskStorage and NetworkStorage available to other crates with a convenient, short path.

  • For the most part, only items that appear in a module need to be use’d. However, a trait must be in scope to call any methods on that trait, even if a type implementing that trait is already in scope. For example, to use the read_to_string method on a type implementing the Read trait, you need to use std::io::Read.

  • The use statement can have a wildcard: use std::io::*. This is discouraged because it is not clear which items are imported, and those might change over time.