Unexpected Golang behaviors

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title: time.RFC3339 is not a valid time.RFC3339 format description: Just a stupid curiosity that will never affect your productivity —-


You may know that there’s a time.Parse(layout, value string) (time.Time, error) function and that there are some pre-defined layouts in the time package like time.RFC3339, for instance.

So, so on one sunny day you decide to use some default value for a RFC3339 timestamp in one of your tests, and first value that comes to your mind is the time.RFC3339 constant which value is

    // ...
    RFC3339     = "2006-01-02T15:04:05Z07:00"
    // ...

So if you don’t pay a lot of attention, you may think that you can parse time.RFC3339 with time.RFC3339 as the layout, but you actually can’t:

package main

import (

func main() {
	_, err := time.Parse(time.RFC3339, time.RFC3339)
	if err != nil {


panic: parsing time "2006-01-02T15:04:05Z07:00": extra text: 07:00


Because the layout itself is not a valid timestamp, since it includes both UTC (Z) and timezone definition (07:00), while the timestamp should include only one of them.