struct Years(i64); struct Days(i64); impl Years { pub fn to_days(&self) -> Days { Days(self.0 * 365) } } impl Days { /// truncates partial years pub fn to_years(&self) -> Years { Years(self.0 / 365) } } fn old_enough(age: &Years) -> bool { age.0 >= 18 } fn main() { let age = Years(5); let age_days = age.to_days(); println!("Old enough {}", old_enough(&age)); println!("Old enough {}", old_enough(&age_days.to_years())); }