将参数传递给方法时出现错误“调用中的附加参数”

北欧海盗第二

我试图快速编写以下Objective-C代码：

NSCalendar *cal = [NSCalendar currentCalendar];
NSDate *now = [NSDate date];
NSDate *startOfTheWeek;
NSTimeInterval interval;
[cal rangeOfUnit:NSWeekCalendarUnit 
       startDate:&startOfTheWeek 
        interval:&interval 
         forDate:now];

它将把本周的开始写到startOfTheWeek，将周的持续时间写到interval。

我在操场上写

let now:NSDate = NSDate()
var startDate:NSDate
var duration: NSTimeInterval // also tried "var duration: CMutablePointer<NSTimeInterval>"
let cal = NSCalendar.currentCalendar()
cal.rangeOfUnit(unit: NSCalendarUnit.WeekCalendarUnit, startDate: startDate, interval: duration, forDate: now)"

尽管代码完成告诉我签名是

cal.rangeOfUnit(<#unit: NSCalendarUnit#>, startDate: AutoreleasingUnsafePointer<NSDate?>, interval: <#CMutablePointer<NSTimeInterval>#>, forDate: <#NSDate?#>)

发生错误，说 Extra argument 'interval' in call

我究竟做错了什么？

我也试过了

cal.rangeOfUnit(NSCalendarUnit.WeekCalendarUnit, startDate: startDate, interval: duration, forDate: now)

但这会产生错误

“找不到接受提供的参数的'rangeOfUnit'的重载。”

让·菲利普·佩莱特

试试这个：

let now = NSDate()
var startDate: NSDate? = nil
var duration: NSTimeInterval = 0
let cal = NSCalendar.currentCalendar()

cal.rangeOfUnit(NSCalendarUnit.WeekCalendarUnit, startDate: &startDate,
    interval: &duration, forDate: now)

（默认情况下，第一个参数没有外部名称，因此不应命名。）

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