Question

有什么方法可以简化这个：

var unloadedImagesRows = [String:[Int]]()

private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    if unloadedImagesRows[forLocation] == nil {
                    unloadedImagesRows[forLocation] = [Int]()
    }
    unloadedImagesRows[forLocation]!.append(row)
}

没有Swift有一种简单的方法来检查nil，如果是，创建一个新对象，所有后续使用都引用该对象？

Answer 1

您可以将其简化为一行：

private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    unloadedImagesRows[forLocation] = (unloadedImagesRows[forLocation] ?? []) + [row]
}

Answer 2

您可以为nil检查创建一个帮助程序运算符，并像下面一样使用它。

infix operator ?= { associativity left precedence 160 }

func ?=<T: Any>(inout left: T?, right: T) -> T {
    if let left = left {
        return left
    } else {
        left = right
        return left!
    }
}

如果为空

，您可以像unloadedImagesRows[forLocation] ?= [Int]()一样使用它

var unloadedImagesRows = [String:[Int]]()

private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    unloadedImagesRows[forLocation] ?= [Int]()
    unloadedImagesRows[forLocation]!.append(row)
}

addToUnloadedImagesRow(1, forLocation: "This is something")

print(unloadedImagesRows) // "["This is something": [1]]\n"

Answer 3

如果您想避开if或guard，可以尝试nil coalescing operator (??)。

private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    var rowsForLocation = unloadedImagesRows[forLocation] ?? [Int]();
    rowsForLocation.append(row)
    unloadedImagesRows[forLocation] = rowsForLocation
}

注意： 这可能效率不高，因为您必须将数组重新分配给字典。我不确定这是否会产生数组的完整副本。

Answer 4

你可以使用if let或guard statement

  private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
      if let a = unloadedImagesRows[forLocation] as? [Int] {
           //...success block
      }
  }

或使用保护声明

  private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
      guard let a = unloadedImagesRows[forLocation] else {
           return
      }
      //...
  }

了解更多信息。检查此link

Answer 5

您可以按照以下方式进行检查。

private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    if let image = unloadedImagesRows[forLocation] {
                //it is not nil
    } else {
        //it is nil
    }

}

Answer 6

var unloadedImagesRows = [String:[Int]]()

// if let
private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    if let _ = unloadedImagesRows[forLocation] {

    } else {
        unloadedImagesRows[forLocation] = [Int]()
    }
    unloadedImagesRows[forLocation]!.append(row)
}

// guard let
private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    guard let _ = unloadedImagesRows[forLocation] else {
        unloadedImagesRows[forLocation] = [Int]()
        return addToUnloadedImagesRow(row, forLocation: forLocation)
    }

    unloadedImagesRows[forLocation]!.append(row)
}

// nil coalescing
private func addToUnloadedImagesRow(row: Int, forLocation:String!) {
    var b = unloadedImagesRows[forLocation] ?? [Int]()
    b.append(row)
    unloadedImagesRows[forLocation] = b
}

Swift语言：nil检查，如果是，则实例化新对象

6 个答案: