斯威夫特3：内部分机设置时间

Question

我必须出现在斯威夫特3不再工作，这种内部日期延长：

internal extension DateComponents { 
    func to12pm() { 
     self.hour = 12 
     self.minute = 0 
     self.second = 0 
    } 
} 

的错误信息是：

Cannot assign to property: 'self' is immutable

如何实现这在Swift 3中？

附加信息（如果需要）：

func endOfWeek(_ weekday: Int) -> Date? { 
    guard 
     let cal = Calendar.current, 
     var comp: DateComponents = (cal as Calendar).components([.weekOfYear], from: self) 
     else { 
      return nil 
    } 
    comp.weekOfYear = 1 
    comp.day -= 1 
    comp.to12pm() 
    return (cal as NSCalendar).date(byAdding: comp, to: self.startOfWeek(weekday)!, options: [])! 
} 

现在看起来是这样的斯威夫特3：

func endOfWeek(_ weekday: Int) -> Date? { 
    let cal = Calendar.current 
    var comp = cal.dateComponents([.weekOfYear], from: self) 
    comp.weekOfYear = 1 
    comp.day? -= 1 
    //This does not have the "comp.to12pm()" that the Swift 2 version did 
    return cal.date(byAdding: comp, to: self.startOfWeek(weekday)!)! 
} 

Answer 1

DateComponents现在是一个结构，多数民众赞成它是由这个日期扩展名为为什么它抛出那个错误：

Cannot assign to property: 'self' is immutable

你n eed从自己创建一个新的变种，改变它并返回它如下：

extension DateComponents { 
    var to12pm: DateComponents { 
     var components = self 
     components.hour = 12 
     components.minute = 0 
     components.second = 0 
     components.nanosecond = 0 
     return components 
    } 
}