How to Convert a Day of Week String to a time.Weekday Value in Go?

Convert a Day of Week String to a time.Weekday Value

In Go, you may encounter the need to convert a string representing a day of the week to its corresponding time.Weekday value.

One approach is to use an array like so:

<code class="go">var daysOfWeek = [...]string{
    "Sunday",
    "Monday",
    "Tuesday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday",
}

func parseWeekday(v string) (time.Weekday, error) {
    for i := range daysOfWeek {
        if daysOfWeek[i] == v {
            return time.Weekday(i), nil
        }
    }

    return time.Sunday, fmt.Errorf("invalid weekday '%s'", v)
}</code>

An Alternative Approach Using a Map

For improved efficiency and ease of lookup, a map is a more idiomatic choice:

<code class="go">var daysOfWeek = map[string]time.Weekday{
    "Sunday":    time.Sunday,
    "Monday":    time.Monday,
    "Tuesday":   time.Tuesday,
    "Wednesday": time.Wednesday,
    "Thursday":  time.Thursday,
    "Friday":    time.Friday,
    "Saturday":  time.Saturday,
}

func parseWeekday(v string) (time.Weekday, error) {
    if d, ok := daysOfWeek[v]; ok {
        return d, nil
    }

    return time.Sunday, fmt.Errorf("invalid weekday '%s'", v)
}</code>

Additional Parsing Options

Using a map allows you to extend the supported weekdays to include abbreviated forms:

<code class="go">for d := time.Sunday; d <= time.Saturday; d++ {
    name := d.String()
    daysOfWeek[name] = d
    daysOfWeek[name[:3]] = d
}</code>

This enables parsing both full and abbreviated weekday strings, e.g., "Monday" and "Mon".

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