Golang : minus time with Time.Add() or Time.AddDate() functions to calculate past date

Let's go back into history for this tutorial's sake. Somehow you have invented a time traveling device powered by Golang and you are wanted to calculate the time when you suppose to end up in the past.

However, Golang has Time.Add() function to calculate future dates and no Minus() function to calculate past dates. So, how does one calculates past dates in Golang?

Solution:

Yes, the word Add can be very limiting; however, do not let the Time.Add() function name fools you. You still can calculate the past date by adding the present with a negative value. If Time.Add() is to cumbersome. You can use Time.AddDate() function as well.

For example:

 package main

 import (
 "fmt"
 "time"
 )

 func main() {
 today := time.Now()
 fmt.Println("Today is : ", today.Format("2006-01-02 03:04:00pm"))

 // travel back 1 day
 oneDay := time.Hour * -24 // minus 1 day

 yesterday := today.Add(oneDay) // minus 1 day
 fmt.Println("Yesterday is : ", yesterday.Format("2006-01-02 03:04:00pm"))

 // for easier calculation, use AddDate() function instead

 sevenDaysAgo := today.AddDate(0, 0, -7) // minus 7 days
 fmt.Println("Seven days ago is : ", sevenDaysAgo.Format("2006-01-02 03:04:00pm"))

 oneYearAgo := today.AddDate(-1, 0, 0) // minus one year
 fmt.Println("One year ago is : ", oneYearAgo.Format("2006-01-02 03:04:00pm"))

 }

Sample output:

Today is : 2016-06-14 01:08:00pm

Yesterday is : 2016-06-13 01:08:00pm

Seven days ago is : 2016-06-07 01:08:00pm

One year ago is : 2015-06-14 01:08:00pm

Hope this helps and happy coding!

References:

https://golang.org/pkg/time/#Time.Add

https://golang.org/pkg/time/#Time.AddDate

https://www.socketloop.com/tutorials/golang-calculate-future-date-with-time-add-function