lifetimes are not the only way to check safety. you just need to detect conflicts in the data dependency graph, lifetimes are in some way an overspecification (for safety, there are autoaliasing advantages). i suspect agnostic conflict detection is probably more expensive, too, but 1) borrow checking was not the slow step in rust compilation and 2) maybe you dont have to check for memory safety on every compile. on commit or on ci is probably fine