DateTime.LastDayOfMonth

RolfG

Is it possible that you implement a datetime.LastDayOfMonth with datetime?
Of course one can implement a datetime extension, but I think this would be more performant, not?

bgrommes

RolfG Or maybe DaysInMonth.

Typically how I do this in C# is:

int DaysInMonth(DateTime someDate) {
    DateTIme firstOfMonth = new Date(someDate.Year,someDate.Month,1);
    return firstOfMonth.AddMonth(1).AddDays(-1).Day;
}

That does seem like quite a bit of thrashing about to get a value and if you need it frequently I agree -- even if the VM has to do something similar and cache the result on first call, it can probably be quicker about it. Plus -- ease of use.

RolfG

At the moment I calculate it "bare-metal":

Public Function LastDayOfMonth(Extends d As DateTime) As integer
 Var monthdays() As Integer = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
 Var result As Integer = monthdays[d.Month]

  # Nur für Februar muss die Logik angewendet werden
  If d.Month = 2 Then
    # Die mathematisch kompakteste Form der Schaltjahr-Prüfung
    If (d.Year Mod 4 = 0 And d.Year Mod 100 <> 0) Or (d.Year Mod 400 = 0) Then
      result = 29
    End If
  End If

 Return result

End Function

Garry

Good suggestion. I’ve implemented this as a read-only DateTime.DaysInMonth property:

Var d As DateTime = New DateTime(2024, 2, 10)
Print(d.DaysInMonth) # 29

It returns an Integer from 28 to 31 for the value’s month and year, including the correct leap-year result.

I chose DaysInMonth rather than LastDayOfMonth because the latter could imply that it returns another DateTime. The implementation is native, so applications no longer need to construct an array or duplicate the leap-year calculation in an extension.

This will be included in the next release. Thanks @RolfG and @bgrommes!

https://feedback.objo.dev/feature/1259