Lifetimes

A borrowed value has a lifetime:

The lifetime can be implicit: add(p1: &Point, p2: &Point) -> Point.
Lifetimes can also be explicit: &'a Point, &'document str.
Read &'a Point as "a borrowed Point which is valid for at least the lifetime a".
Lifetimes are always inferred by the compiler: you cannot assign a lifetime yourself.
- Lifetime annotations create constraints; the compiler verifies that there is a valid solution.
Lifetimes for function arguments and return values must be fully specified, but Rust allows lifetimes to be elided in most cases with a few simple rules.