Summary

You are allowed to borrow references to values

Borrowing a reference does not move ownership

Borrowing is the preferred way to solve the “move in move out” problem we encountered previously

References have their own type, and i32 is different than &i32

We also have mutable references such as &mut i32, which allow the values behind the reference to be changed

Mutable references can only be borrowed from mutable values

References are, essentially, addresses for where the original value lives in memory

If you want to operate directly on the value behind a reference, you can dereference using the * operator

A reference cannot outlive the value it refers to

To avoid confusion around mutation and references, Rust has some rules you need to abide by

• You cannot mutate a value if there is a reference to it

• You can have multiple immutable references to a value

• You can only have one mutable reference to a value, and then no other immutable references to it, or access the value directly

You can create an immutable reference from a mutable reference, but not the other way around.