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Paths

A path is a sequence of one or more path components logically separated by a namespace qualifier (::). If a path consists of only one component, it may refer to either an item or a variable in a local control scope. If a path has multiple components, it refers to an item.

Every item has a canonical path within its crate, but the path naming an item is only meaningful within a given crate. There is no global namespace across crates; an item's canonical path merely identifies it within the crate.

Two examples of simple paths consisting of only identifier components:

x;
x::y::z;

Path components are usually identifiers, but they may also include angle-bracket-enclosed lists of type arguments. In expression context, the type argument list is given after a :: namespace qualifier in order to disambiguate it from a relational expression involving the less-than symbol (<). In type expression context, the final namespace qualifier is omitted.

Two examples of paths with type arguments:

# #![allow(unused_variables)]
#fn main() {
# struct HashMap<K, V>(K,V);
# fn f() {
# fn id<T>(t: T) -> T { t }
type T = HashMap<i32,String>; // Type arguments used in a type expression
let x  = id::<i32>(10);       // Type arguments used in a call expression
# }

#}

Paths can be denoted with various leading qualifiers to change the meaning of how it is resolved:

  • Paths starting with :: are considered to be global paths where the components of the path start being resolved from the crate root. Each identifier in the path must resolve to an item.
mod a {
    pub fn foo() {}
}
mod b {
    pub fn foo() {
        ::a::foo(); // call a's foo function
    }
}
# fn main() {}
  • Paths starting with the keyword super begin resolution relative to the parent module. Each further identifier must resolve to an item.
mod a {
    pub fn foo() {}
}
mod b {
    pub fn foo() {
        super::a::foo(); // call a's foo function
    }
}
# fn main() {}
  • Paths starting with the keyword self begin resolution relative to the current module. Each further identifier must resolve to an item.
fn foo() {}
fn bar() {
    self::foo();
}
# fn main() {}

Additionally keyword super may be repeated several times after the first super or self to refer to ancestor modules.

mod a {
    fn foo() {}

    mod b {
        mod c {
            fn foo() {
                super::super::foo(); // call a's foo function
                self::super::super::foo(); // call a's foo function
            }
        }
    }
}
# fn main() {}

© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/reference/paths.html