Module chrono::naive::time

ISO 8601 time without timezone.

Leap Second Handling

Since 1960s, the manmade atomic clock has been so accurate that it is much more accurate than Earth's own motion. It became desirable to define the civil time in terms of the atomic clock, but that risks the desynchronization of the civil time from Earth. To account for this, the designers of the Coordinated Universal Time (UTC) made that the UTC should be kept within 0.9 seconds of the observed Earth-bound time. When the mean solar day is longer than the ideal (86,400 seconds), the error slowly accumulates and it is necessary to add a leap second to slow the UTC down a bit. (We may also remove a second to speed the UTC up a bit, but it never happened.) The leap second, if any, follows 23:59:59 of June 30 or December 31 in the UTC.

Fast forward to the 21st century, we have seen 26 leap seconds from January 1972 to December 2015. Yes, 26 seconds. Probably you can read this paragraph within 26 seconds. But those 26 seconds, and possibly more in the future, are never predictable, and whether to add a leap second or not is known only before 6 months. Internet-based clocks (via NTP) do account for known leap seconds, but the system API normally doesn't (and often can't, with no network connection) and there is no reliable way to retrieve leap second information.

Chrono does not try to accurately implement leap seconds; it is impossible. Rather, it allows for leap seconds but behaves as if there are no other leap seconds. Various time arithmetics will ignore any possible leap second(s) except when the operand were actually a leap second. The leap second is indicated via fractional seconds more than 1 second, so values like NaiveTime::from_hms_milli(23, 56, 4, 1_005) are allowed; that value would mean 5ms after the beginning of a leap second following 23:56:04. Parsing and formatting will correctly handle times that look like leap seconds, and you can then conveniently ignore leap seconds if you are not prepared for them.

If you cannot tolerate this behavior, you must use a separate TimeZone for the International Atomic Time (TAI). TAI is like UTC but has no leap seconds, and thus slightly differs from UTC. Chrono 0.2 does not provide such implementation, but it is planned for 0.3.

Structs

NaiveTime

ISO 8601 time without timezone. Allows for the nanosecond precision and optional leap second representation.