How to Get the Local Start of Day in Go?

Locating the Beginning of a Local Day

To retrieve a local start-of-day time object, a common approach is to extract the year, month, and day components and reconstruct the date. However, is there a more orthodox function provided by the standard library?

The following snippet demonstrates a custom Bod function that performs this task:

func Bod(t time.Time) time.Time {
    year, month, day := t.Date()
    return time.Date(year, month, day, 0, 0, 0, 0, t.Location())
}

While the Bod function correctly determines the local start of today, the Truncate function, which is suggested as an alternative, provides a different result. To scrutinize this, consider the following code:

chicago, err := time.LoadLocation("America/Chicago")
if err != nil {
    fmt.Println(err)
    return
}
now := time.Now().In(chicago)
fmt.Println(Bod(now))
fmt.Println(Truncate(now))

This code generates the following output:

2014-08-11 00:00:00 -0400 EDT
2014-08-11 20:00:00 -0400 EDT

It becomes evident that the Truncate method operates on UTC time, while the Bod function maintains the local time (Chicago). Furthermore, Truncate assumes a constant 24-hour day, which is inaccurate for locations like Chicago that experience daylight saving time variations.

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