Understanding Duration in time package in Go (Golang)

duration is the time that has elapsed between two instants of time. It is represented as int64nanosecond count. So duration is nothing in Go but just a number representing time in nanoseconds in Go. So if duration value is equal to 1000000000 then it represents 1 sec or 1000 milliseconds or 10000000000 nanoseconds. Since duration is int64, the largest duration that can be represented is 290 years apart. So duration is used to capture the number of nanoseconds between two time.Time objects. As an example duration between two time values 1 hour apart will be below value which is equal to the number of nanoseconds in 1 hour.

1 *60*60*1000*1000*1000

It is represented as below in the time package.

type Duration int64

Below are some common duration which are defined in time package

const (
    Nanosecond  Duration = 1
    Microsecond          = 1000 * Nanosecond
    Millisecond          = 1000 * Microsecond
    Second               = 1000 * Millisecond
    Minute               = 60 * Second
    Hour                 = 60 * Minute
)

Some of the function defined on time.Time object that returns the Duration are

• func (t Time) Sub(u Time) Duration – It returns the duration t-u
• func Since(t Time) Duration – It returns the duration which has elapsed since t
• func Until(t Time) Duration – It returns the duration until t

type Duration also defines several utility function which can be used to convert a duration value to-

• Hours
• Minutes
• Seconds

The print value of duration is represented as in the form “10h8m0.5s” where h representing hour, m representing minute and s representing seconds respectively

Let’s see a working code of what we have learned so far

package main

import (
    "fmt"
    "time"
)

func main() {
    now := time.Now()
    oldTime := time.Date(2020, 1, 2, 0, 0, 0, 0, time.UTC)
    diff := now.Sub(oldTime)
    //diff is of type Duration now
    
    //In hours
    fmt.Printf("Hours: %f\n", diff.Hours())

    //In minutes
    fmt.Printf("Minutes: %f\n", diff.Minutes())

    //In seconds
    fmt.Printf("Seconds: %f\n", diff.Seconds())

    //time Since
    fmt.Println(time.Since(now.Add(-time.Hour * 1)))

    //time until
    fmt.Println(time.Until(now.Add(time.Hour * 1)))
}

Output:

Hours: 714.565222
Minutes: 42873.913306
Seconds: 2572434.798350
1h0m0.000093629s
59m59.999888401s