References

References let you pass a way to access a value to a function without copying the value. &identifier is a reference to the identifier value, &Person is a type that is a reference to the Person type. To go from a reference to the value dereference let bob = *bob_ref, but this happens automatically with 'autoderef'.

References are stack allocated pointers to values in the heap. They represent a borrowed value. 


#![allow(unused)]
fn main() {
let a = 1;
let referenceToA: &i32 = &a;
let mutableReferenceToA = &mut a;
}

Dereferencing

* is the inverse of &. 


#![allow(unused)]
fn main() {
let a = 1;
let a_ref = &a;
let b = *a_ref;
}

The 'dot' operator . dereferences automatically.

Mutable References


#![allow(unused)]
fn main() {
let mut identifier = 1;
let mut_ref = &mut identifier; // this is a mutable reference. Mutable borrow. 
}

There can be only one mutable reference, and it cannot be in scope with an immutable reference.

More on passing to functions and mutability

  • fn function_name(variable: String) takes a String and owns it. If it doesn't return anything, then the variable dies inside the function.
  • fn function_name(variable: &String) borrows a String and can look at it
  • fn function_name(variable: &mut String) borrows a String and can change it