Lesson 19 · Local dates and local times

Local dates and local times

Not every timestamp needs both a date and a time. Today you parse the two remaining datetime forms, a local date on its own and a local time on its own, completing the four-way classification.

The goal

Parse a local date, a local time, and a fractional-second time.

Start here - the target

TO DO

Scenario: Date-only and time-only values

Giventhe value 1979-05-27 and the value 07:32:00 and the value 00:32:00.999999

Whenthey are parsed

Thenthe first is a local date (year 1979, month 5, day 27, no time), the second is a local time (07:32:00, no date), and the third is a local time whose fractional second is 999999000 nanoseconds

Andthe four datetime kinds are told apart by shape: date then time gives a date-time, date alone gives a local date, time alone gives a local time, and a trailing offset makes it an offset date-time

Background

The two full-timestamp forms have shorter siblings. A local date is a calendar day with no time at all, like 1979-05-27 - a birthday, a release date. A local time is a time of day with no date, like 07:32:00 - a daily alarm, an opening hour. Both reuse the field extraction from the previous lesson; they just fill in fewer parts and leave HasTime or HasDate false.

This completes a four-way classification by shape. When the value has a leading sign or is all digits with an optional . or e, it is a number. Otherwise, a date part (YYYY-MM-DD) followed by a time part is a date-time - offset if a timezone trails it, local if not; a date part alone is a local date; and a time part (HH:MM:SS) alone is a local time. Times may carry a fractional second, and TOML records it to nanosecond precision, so .999999 becomes 999999000 nanoseconds. With these four forms plus the numbers and booleans, every TOML scalar value now parses.

Make it work

// classify a numeric token by its shape:
//   has a date part and a time part -> (offset?) date-time
//   matches YYYY-MM-DD only          -> KindLocalDate
//   matches HH:MM:SS(.fff) only       -> KindLocalTime
// a fraction after seconds: scale to nanoseconds (.999999 -> 999999000)

CheckpointDONE

Local dates and local times parse, completing the datetime forms. Commit and stop here.