[−][src]Keyword mut
A mutable variable, reference, or pointer.
mut
can be used in several situations. The first is mutable variables,
which can be used anywhere you can bind a value to a variable name. Some
examples:
// A mutable variable in the parameter list of a function. fn foo(mut x: u8, y: u8) -> u8 { x += y; x } // Modifying a mutable variable. let mut a = 5; a = 6; assert_eq!(foo(3, 4), 7); assert_eq!(a, 6);Run
The second is mutable references. They can be created from mut
variables
and must be unique: no other variables can have a mutable reference, nor a
shared reference.
// Taking a mutable reference. fn push_two(v: &mut Vec<u8>) { v.push(2); } // A mutable reference cannot be taken to a non-mutable variable. let mut v = vec![0, 1]; // Passing a mutable reference. push_two(&mut v); assert_eq!(v, vec![0, 1, 2]);Run
ⓘ
let mut v = vec![0, 1]; let mut_ref_v = &mut v; #[allow(unused)] let ref_v = &v; mut_ref_v.push(2);Run
Mutable raw pointers work much like mutable references, with the added
possibility of not pointing to a valid object. The syntax is *mut Type
.
More information on mutable references and pointers can be found in``` Reference.