Get the number of days between two dates in Go

Recently I needed to find the number of days between two dates in Go and kept coming across implementations that didn't quite suit my needs.

So I rolled my own, and I'm pretty proud of how robust it is! :)

package main

import (
    "fmt"
    "time"
)

func main() {
    fmt.Println(daysBetween(date("2012-01-01"), date("2012-01-07"))) // 6
    fmt.Println(daysBetween(date("2016-01-01"), date("2017-01-01"))) // 366 because leap year
    fmt.Println(daysBetween(date("2017-01-01"), date("2018-01-01"))) // 365
    fmt.Println(daysBetween(date("2016-01-01"), date("2016-01-01"))) // 0
}

func daysBetween(a, b time.Time) int {
    if a.After(b) {
        a, b = b, a
    }

    days := -a.YearDay()
    for year := a.Year(); year < b.Year(); year++ {
        days += time.Date(year, time.December, 31, 0, 0, 0, 0, time.UTC).YearDay()
    }
    days += b.YearDay()

    return days
}

func date(s string) time.Time {
    d, _ := time.Parse("2006-01-02", s)
    return d
}