Sure, these aren't for defensive programming—they're for places where you know a location is unreachable, but your compiler can't prove it for you. The example

Sure, these aren't for defensive programming—they're for places where you know a location is unreachable, but your compiler can't prove it for you. The example given in the rust docs, for example, is a match clause with complete guard arms (i.e. if n < 0 and if n >= 0).