golang 时间的比较，time.Time的初始值？

参考： https://golangcode.com/checking-if-date-has-been-set/

https://stackoverflow.com/questions/20924303/date-time-comparison-in-golang

// utc life
loc, _ := time.LoadLocation("UTC")

// setup a start and end time
createdAt := time.Now().In(loc).Add(1 * time.Hour)
expiresAt := time.Now().In(loc).Add(4 * time.Hour)

// get the diff
diff := expiresAt.Sub(createdAt)
fmt.Printf("Lifespan is %+v", diff)

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Check If a Date/Time Has Been Set with IsZero

Feb 16, 2019 · 175 words · 1 minute read

#DATE #TIME #ZERO #ISSET #NIL #TIMESTAMP #STATE

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In Go, we can store and use dates using the time package and although a date in Go cannot be saved as null (because there’s no such thing) there is an unset state. This unset state can be shown as 0001-01-01 00:00:00 +0000 UTC and there’s a simple way we can check if a date variable has been populated, as demonstrated below. It’s also important to note that these are not unix timestamps, which go back as far as 1970, but can handle a large spectrum of dates.

package main

import (
    "fmt"
    "time"
)

func main() {

    var myDate time.Time

    // IsZero returns a bool of whether a date has been set, but as the printf shows it will
    // still print a zero-based date if it hasn't been set.
    if myDate.IsZero() {
        fmt.Printf("No date has been set, %s\n", myDate)
    }

    // Demonstrating that by setting a date, IsZero now returns false
    myDate = time.Date(2019, time.February, 1, 0, 0, 0, 0, time.UTC)
    if !myDate.IsZero() {
        fmt.Printf("A date has been set, %s\n", myDate)
    }
}

Use the time package to work with time information in Go.

Time instants can be compared using the Before, After, and Equal methods. The Sub method subtracts two instants, producing a Duration. The Add method adds a Time and a Duration, producing a Time.

Play example:

package main

import (
    "fmt"
    "time"
)

func inTimeSpan(start, end, check time.Time) bool {
    return check.After(start) && check.Before(end)
}

func main() {
    start, _ := time.Parse(time.RFC822, "01 Jan 15 10:00 UTC")
    end, _ := time.Parse(time.RFC822, "01 Jan 16 10:00 UTC")

    in, _ := time.Parse(time.RFC822, "01 Jan 15 20:00 UTC")
    out, _ := time.Parse(time.RFC822, "01 Jan 17 10:00 UTC")

    if inTimeSpan(start, end, in) {
        fmt.Println(in, "is between", start, "and", end, ".")
    }

    if !inTimeSpan(start, end, out) {
        fmt.Println(out, "is not between", start, "and", end, ".")
    }
}