Why use AA when you can array?

```D
    static immutable dayOfWeekStrings = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
    static immutable monthStrings     = ["Jan", "Feb", "Mar", "Apr",  "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

    string dayOfWeekStr = dayOfWeekStrings[dayOfWeek];
    string monthStr     = monthStrings[month - 1];
```

I'd doubt you can get much more efficient than that.