How to Convert a String Representation of a Day of Week into a `time.Weekday` Value?

Parse String Representation of Day of Week into time.Weekday Value

Problem:

Converting a string representing a day of the week into an equivalent time.Weekday value presents a challenge. The time package does not include any built-in functionality for this conversion.

Initial Solution:

An initial approach is to utilize an array to store the mapping between day of week strings and their corresponding time.Weekday values. For instance:

<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>

Recommended Optimization:

To enhance the efficiency and clarity of this conversion, a map is recommended instead of an array. Maps allow for faster lookups, resulting in improved performance.

<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>

Tip:

For a robust solution, a for loop can be employed to safely initialize the daysOfWeek map.

<code class="go">var daysOfWeek = map[string]time.Weekday{}

func init() {
    for d := time.Sunday; d <= time.Saturday; d++ {
        daysOfWeek[d.String()] = d
    }
}</code>

Additional Parsing Flexibility:

The map-based solution offers an advantage over the array-based approach. By adding additional key-value pairs to the map, additional valid values can be parsed without modifying the parsing logic.

For instance, to parse both the full and 3-letter short names of weekdays, the map can be extended as follows:

<code class="go">var daysOfWeek = map[string]time.Weekday{}

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

This extended solution allows for parsing strings like "Mon" or "Fri" into their corresponding time.Weekday values.

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