let calendar = Calendar.current
let components = calendar.dateComponents([.year, .month], from: Date())
let startOfMonth = calendar.date(from: components)! // 시작날짜
let numberOfDays = calendar.range(of: .day, in: .month, for: startOfMonth)!.upperBound // 해당 달의 총 날짜
let allDays = Array(1..<numberOfDays).map{ calendar.date(byAdding:.day, value: $0, to: startOfMonth)!} // 각 날짜별 Date객체 생성 후 배열에 저장

allDays.forEach { (element) in
  let componentEach = calendar.dateComponents([.weekday], from: element)
  //componentEach.weekday의 value는 1~7의 optional value
  if componentEach.weekday == 7 {
    print("WEEKDAY 7 : \(element)")
  }else{
    print("NO : \(element)")
  }
}