Simple Zero Sized Typed Utc timezones for [chrono]. This needs const generic (for rust >= 1.51 in stable). use chrono::*; use chrono_simpletz::UtcZst; use chrono_simpletz::known_timezones::*; use std::mem::size_of_val; //constract by new() or Default::default() let p9 = UtcP9::new(); //size of UtcP9 is zero assert_eq!(size_of_val(&p9), 0); assert_eq!(&p9.to_string(), "+09:00"); assert_eq!(UtcP9::IS_IN_VALID_RANGE, true); let time = p9.ymd(2000, 1, 1).and_hms(12, 00, 00); let naive_time = NaiveDate::from_ymd(2000, 1, 1).and_hms(3, 0, 0); assert_eq!(time.naive_utc(), naive_time); //same size as naive datetime assert_eq!(size_of_val(&time),size_of_val(&naive_time)); let fixed = time.with_timezone(&p9.fix()); assert_eq!(time, fixed); //same Display with FixedOffset assert_eq!(time.to_string(), fixed.to_string()); // smaller size than fixed size assert!(size_of_val(&time) < size_of_val(&fixed) )