The final line "assert!(i.get());" asserts that i.get() is true in the end. The ! character here belongs to the assert! macro, not a boolean negation. (This unf

The final line "assert!(i.get());" asserts that i.get() is true in the end. The ! character here belongs to the assert! macro, not a boolean negation. (This unfortunately gets a bit weird-looking when you want to write sensible stuff like "if !matches!(x, Some(5..=10)) { ... }".)