TTuck
Time and numbers · Example 64

Time

fmt time

Go offers extensive support for times and durations; here are some examples.

package main

import (
	"fmt"
	"time"
)

func main() {
	p := fmt.Println

We'll start by getting the current time. Its value changes on every run, so we only print its type here.

	now := time.Now()
	fmt.Printf("now is a %T\n", now)

You can build a time struct by providing the year, month, day, etc. Times are always associated with a Location, i.e. time zone.

	then := time.Date(
		2009, 11, 17, 20, 34, 58, 651387237, time.UTC)
	p(then)

You can extract the various components of the time value as expected.

	p(then.Year())
	p(then.Month())
	p(then.Day())
	p(then.Hour())
	p(then.Minute())
	p(then.Second())
	p(then.Nanosecond())
	p(then.Location())

The Monday-Sunday Weekday is also available.

	p(then.Weekday())

These methods compare two times, testing if the first occurs before, after, or at the same time as the second, respectively.

	later := then.Add(48 * time.Hour)
	p(then.Before(later))
	p(then.After(later))
	p(then.Equal(later))

The Sub methods returns a Duration representing the interval between two times.

	diff := later.Sub(then)
	p(diff)

We can compute the length of the duration in various units.

	p(diff.Hours())
	p(diff.Minutes())
	p(diff.Seconds())
	p(diff.Nanoseconds())

You can use Add to advance a time by a given duration, or with a - to move backwards by a duration.

	p(then.Add(diff))
	p(then.Add(-diff))

AddDate moves by calendar units, and Truncate rounds down to a multiple of a duration.

	p(then.AddDate(0, 1, 0))
	p(then.Truncate(time.Hour))

Durations parse from strings like "1h30m", and convert between zones with In.

	d, _ := time.ParseDuration("1h15m30.5s")
	p(d, d.Round(time.Minute))
	tokyo, err := time.LoadLocation("Asia/Tokyo")
	if err == nil {
		p(then.In(tokyo))
	}

time.Since measures elapsed time; it's the usual way to time a piece of code.

	start := time.Now()
	time.Sleep(10 * time.Millisecond)
	p("elapsed at least 10ms:", time.Since(start) >= 10*time.Millisecond)
}
$ go run ./64_time
now is a time.Time
2009-11-17 20:34:58.651387237 +0000 UTC
2009
November
17
20
34
58
651387237
UTC
Tuesday
true
false
false
48h0m0s
48
2880
172800
172800000000000
2009-11-19 20:34:58.651387237 +0000 UTC
2009-11-15 20:34:58.651387237 +0000 UTC
2009-12-17 20:34:58.651387237 +0000 UTC
2009-11-17 20:00:00 +0000 UTC
1h15m30.5s 1h16m0s
2009-11-18 05:34:58.651387237 +0900 JST
elapsed at least 10ms: true
View on GitHub