Time zones

Each Time has an associated Location, which is used for display purposes.

The method In returns a time with a specific location. Changing the location in this way changes only the presentation; it does not change the instant in time.

Here is a convenience function that changes the location associated with a time.

// TimeIn returns the time in UTC if the name is "" or "UTC".
// It returns the local time if the name is "Local".
// Otherwise, the name is taken to be a location name in
// the IANA Time Zone database, such as "Africa/Lagos".
func TimeIn(t time.Time, name string) (time.Time, error) {
	loc, err := time.LoadLocation(name)
	if err == nil {
		t = t.In(loc)
	}
	return t, err
}

In use:

for _, name := range []string{
	"",
	"Local",
	"Asia/Shanghai",
	"America/Metropolis",
} {
	t, err := TimeIn(time.Now(), name)
	if err == nil {
		fmt.Println(t.Location(), t.Format("15:04"))
	} else {
		fmt.Println(name, "<time unknown>")
	}
}

UTC 19:32
Local 20:32
Asia/Shanghai 03:32
America/Metropolis <time unknown>

Warning: A daylight savings time transition skips or repeats times. For example, in the United States, March 13, 2011 2:15am never occurred, while November 6, 2011 1:15am occurred twice. In such cases, the choice of time zone, and therefore the time, is not well-defined. Date returns a time that is correct in one of the two zones involved in the transition, but it does not guarantee which. Package time: Date

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