Date Extensions for First and Last Day of Month

Date+FirstAndLastDayOfMonth.swift

extension Date
{
    var startOfMonth : Date?
    {
        let calendar     = Calendar.current
        let components   = calendar.dateComponents([.year, .month], from: self)
        let firstDayDate = calendar.date(from: components)

        return firstDayDate
    }

    var startOfNextMonth : Date?
    {
        let calendar   = Calendar.current
        var components = calendar.dateComponents([.year, .month], from: self)

        components.setValue((components.month! + 1), for: .month)

        let firstDayDateOfNextMonth = calendar.date(from: components)

        return firstDayDateOfNextMonth
    }

    var endOfMonth : Date?
    {
        let calendar   = Calendar.current
        var components = calendar.dateComponents([.year, .month], from: self)

        components.setValue((components.month! + 1), for: .month)
        components.setValue(0, for: .day)

        let lastDayDate = calendar.date(from: components)

        return lastDayDate
    }
}

let today     = DateFormatter.localizedString(from: Date(),                   dateStyle: .medium, timeStyle: .none)
let firstDay  = DateFormatter.localizedString(from: Date().startOfMonth!,     dateStyle: .medium, timeStyle: .none)
let lastDay   = DateFormatter.localizedString(from: Date().endOfMonth!,       dateStyle: .medium, timeStyle: .none)
let nextMonth = DateFormatter.localizedString(from: Date().startOfNextMonth!, dateStyle: .medium, timeStyle: .none)

print("""
    \(today) is today's date.
    \(firstDay) is the first day of this month.
    \(lastDay) is the last day of this month.
    \(nextMonth) is the first day of next month.
""")