Get integer month value from string

问题

I'm parsing a cron string from AWS that looks like this cron(0 7 13 November ? 2019). Is there a clean way to go from November back to 11 using Go's built in types? The time.Month type allows mapping int to string, but there doesn't seem to be a way to do the reverse. Am I missing something? For now, I've written this to get a map[string]int that I'm using like this: monthi := getMonths()[monthName].

func getMonths() map[string]int {
    m := make(map[string]int)
    for i := 1; i < 13; i++ {
        month := time.Month(i).String()
        m[month] = i
    }
    return m
}

回答1:

Foreword: I released this utility in github.com/icza/gox, see timex.ParseMonth().

That is currently the best approach.

Best would be to use a package level variable and populate the map only once.

And it's much cleaner and safer to do the population this way:

var months = map[string]time.Month{}

func init() {
    for i := time.January; i <= time.December; i++ {
        months[i.String()] = i
    }
}

Testing it:

for _, s := range []string{"January", "December", "invalid"} {
    m := months[s]
    fmt.Println(int(m), m)
}

Output (try it on the Go Playground):

1 January
12 December
0 %!Month(0)

Note that this map has the flexibility that you may add short month names, mapping to the same month. E.g. you may also add months["Jan"] = time.January, so if your input is "Jan", you would also be able to get time.January. This could easily be done by slicing the long name, in the same loop, for example:

for i := time.January; i <= time.December; i++ {
    name := i.String()
    months[name] = i
    months[name[:3]] = i
}

Also note that it's possible to use time.Parse() to do the parsing where the layout string is "January":

for _, s := range []string{"January", "December", "invalid"} {
    t, err := time.Parse("January", s)
    m := t.Month()
    fmt.Println(int(m), m, err)
}

Which outputs (try it on the Go Playground):

1 January <nil>
12 December <nil>
1 January parsing time "invalid" as "January": cannot parse "invalid" as "January"

But the simple map lookup is superior to this in performance.

See similar question: Parse Weekday string into time.Weekday

来源：https://stackoverflow.com/questions/59681199/get-integer-month-value-from-string

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