What is a good mental model of borrow checker?

[steffahn]

@quinedot

So you need a third rule:

• Reborrows (of references) can outlive the value liveness scope (not the lifetime) of the reborrowee

(I'd argue you need the rule as this is in contrast with most exclusive-chain-of-access situations, where a link's liveness scope ending will invalidate everything beyond it; alternatively you need a rule for all of those. In either case, there are different semantics.)

Haha, right at this very moment a new user asks a question about exactly that behavior

About lifetime, why this code pass?

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str { if x.len() > y.len() { x } else { y } } fn main() { let string2 = String::from("xyzfffssssssssssss"); let string1 = String::from("long string is long"); { //inner scope 1 let result; { // inner scope 2 let str1_ref1= &string1[0..5]; let str2_ref1= &string2[0..5]; result = longest(str1_ref1,str2_ref1); } …

(though that one could also be explained with the Copy behavior of shared references… re-borrows are more relevant for mutable references)