Lifetimes and Regions

function first<'a, T>(values: &'a readonly T[]): &'a readonly T {
    &values[0]
}
- as soon as we pass and store references, we need to make sure those are safe too
- well wouldn't you know, lifetimes
- generalised lifetimes into regions (combine lifetime + space/place)
- T & 'a, 'a & "shared", ...
- Borrowed, REadonlyBorrowed, ExclusiveBorrowed

- stored borrows write lifetime parameters explicitly; function signatures infer hidden lifetime parameters, prefer the receiver lifetime, union borrowed input lifetimes, and otherwise use "static"

- a borrow used to initialize a binding extends its temporary to the binding lifetime; other
temporaries live to the end of the enclosing statement