    Sub WritePersons()
        Dim Filename = "Persons.txt"
        If File.Exists(Filename) Then
            File.Delete(Filename)
        End If
        Dim s As New List(Of String)
        For Each p As Person In Persons
            s.Add($"{p.FirstName}:{p.LastName}:{p.Gender.ToString}")
        Next
        File.AppendAllLines(Filename, s)
    End Sub
    Sub ReadPersons()
        Dim Filename = "Persons.txt"
        If File.Exists(Filename) Then
            Dim lines = File.ReadAllLines(Filename)
            For Each line As String In lines
                Dim fields = line.Split(":"c)
                Dim p As Person
                p.FirstName = fields(0)
                p.LastName = fields(1)
                p.Gender = CType([Enum].Parse(GetType(GenderType), fields(2)), GenderType)
                Persons.Add(p)
            Next
        End If
    End Sub