time in go

README.md

Working with time in Go is pretty straightforward.

Times

Get the current local time:

now := time.Now()                                   // 02 Apr 15 14:03

Construct a time with Date(y, m, d, h, m, s, ns, loc):

y := 2009
m := time.November
d := 10
h := 23
m := 0
s := 0
t := time.Date(y, m, d, h, m, s, 0, time.UTC)       // 10 Nov 09 23:00

Durations

Given a Time, you can add a Duration.

To convert an integer number of time units (seconds, minutes, etc.) to a Duration, just multiply:

now := time.Now()                                   // 02 Apr 15 14:03

mins := 10
later := now.Add(time.Duration(mins) * time.Minute) // 02 Apr 15 14:13

You can also use AddDate(y, m, d) to add a given number of years, months, days:

y := 2
m := 2
d := 2

later := now.AddDate(y, m, d)                       // 04 Jun 17 14:13

Formatting

Various formatting options are pre-defined:

fmt.Println(now.Format(time.RFC822))                // 02 Apr 15 14:03 CDT
fmt.Println(now.Format(time.Kitchen))               // 2:13PM

You can also define your own format with an example layout:

const layout = "Jan 2, 2006 at 3:04pm"
fmt.Println(now.Format(layout))                     // Apr 2, 2015 at 2:13pm

Parsing

You also use layouts for parsing strings representing times:

const shortForm = "2006-01-02"
loc, _ := time.LoadLocation("America/Chicago")

t, _ := time.ParseInLocation(shortForm, "2015-01-19", loc)

The time t is now 2015-01-19 00:00:00 -0600 CST.

Encoding/Decoding

See codec.go example.

codec.go

package main

import (
    "fmt"
    "time"
    "encoding/binary"
)

func main() {

    const shortForm = "2006-01-02"
    loc, _ := time.LoadLocation("America/Chicago")

    t, err := time.ParseInLocation(shortForm, "2015-01-19", loc)
    if err != nil {
        fmt.Println(err)
        return
    }
    d := decode(encode(t))

    fmt.Println(d)
    fmt.Println(d.Format(shortForm))
}

// decode unmarshals a time.
func decode(b []byte) time.Time {
    i := int64(binary.BigEndian.Uint64(b))
    return time.Unix(i, 0)
}

// encode marshals a time.
func encode(t time.Time) []byte {
    buf := make([]byte, 8)
    u := uint64(t.Unix())
    binary.BigEndian.PutUint64(buf, u)
    return buf
}

/*
// see http://stackoverflow.com/a/23695774/546630
type ShortFormTime time.Time

func (s ShortFormTime) UnmarshalJSON(buf []byte) error {
    . . . 
}

func (s ShortFormTime) MarshalJSON() ([]byte, error) {
    t := time.Time(s)
    return []byte(t.Format(`"2006-01-02"`)), nil
}
*/

time.go

package main

import (
    "fmt"
    "time"
)

func main() {
    t0 := time.Now()
    fmt.Println("The time is now ...")
    printTime(t0)

    // To convert an integer number of units to a Duration, just multiply.
    // see `http://golang.org/pkg/time/#Duration`.
    mins := 10
    days := 2

    t1 := t0.Add(time.Duration(mins) * time.Minute)
    fmt.Printf("\n... and in %v minutes the time will be ...\n", mins)
    printTime(t1)

    fmt.Printf("\n... and %v days after that ...\n", days)
    t2 := t1.Add(time.Duration(days) * time.Hour * 24)
    printTime(t2)

    // Use `AddDate(y, m, d)` to add the given number of years, months, days.
    years   := 2
    months  := 2

    fmt.Printf(
        "\n... and %v years, %v months, and %v days after that ...\n", 
        years, months, days,
    )
    t3 := t2.AddDate(years, months, days)
    printTime(t3)

}

func printTime(t time.Time) {
    // see http://golang.org/pkg/time/#pkg-constants
    fmt.Println(t.Format(time.RFC822)) 

    // see http://golang.org/pkg/time/#Time.Format
    const layout = "Jan 2, 2006 at 3:04pm (MST)"
    fmt.Println(t.Format(layout))
}

y := 2009
m := time.November
d := 10
h := 23
m := 0
s := 0
t := time.Date(y, m, d, h, m, s, 0, time.UTC)       // 10 Nov 09 23:00

No, this will give you 10 (0th month) 09 23:00, or probably rather an error before that because you have two "m:=" lines.