Ian K. Guimarães

Rust book - Lifetimes

  • Lifetimes validates a reference exists for as long we need them to
  • Every value has a lifetime, which is the scope that the reference is valid
  • The borrow checker is responsible for ensure the lifetime of each reference is valid in the moment its used
  • Lifetimes annotations are meant to tell the compiler => borrow checker how they relate to other references. So a single generic lifetime annotation would make much sense in a function.
  • The signature below tells the compiler that the return value will be valid as long as both parameters are:
fn longest<'a>(s1: &'a str, s2: &'a str) -> &'a str

  • valid = a >= b && b == c where a is outer scope b is inner scope c is scope where function is defined

  • Every time a function returns a reference it needs to specify the lifetime? No only when the compiler cannot figure out on its own

  • Lifetime elision solves the problem of specifying lifetime annotations on functions that take a reference as param and return that same reference

  • In the struct below, the struct can’t live longer than the reference it holds

struct Book<'a> {
	page: &'a str,
}
  • the 'static lifetime tells the compiler that reference lives forever. That’s the case of string literals, since they’re put directly into the program binary.