Compile error if it's holding on to any borrowed data on the stack - however, borrowing is only the default, if you move from a capture your closure will contai

Compile error if it's holding on to any borrowed data on the stack - however, borrowing is only the default, if you move from a capture your closure will contain that value instead of reference to the value, and if you have "move" in front of your closure, all the captures are contained in the closure, so by boxing or by using -> impl Fn(...) you can safely return it. If you need to hold onto data accessed from multiple locations, you'd need to use Rc<T> instead of keeping that data on the stack, which is closer to GC'd languages (and pretty similar to Swift, IIUC, except Rust is more explicit).