迭代Swift中的NSMutableArray

Question

我试图迭代一个NSMutableArray，它的行为似乎与NSArray不同（至少在XCode 6 beta 3中）

class Element : NSObject { }

let a = NSArray()
let ma = NSMutableArray()

for e in a as Element[] { }
for e in ma as Element[] { } // compiler error: Cannot convert the expression's type 'Element[]' to type 'Element[]'
for e in ma as NSArray as Element[] { }

我很困惑为什么会这样。是否有此行为的解释或这是一个XCode / Swift错误？

Answer 1

好的，让我们改一下来澄清这个问题：

class Element : NSObject { }

// Create NSArray and NSMutableArray objective-c objects
let a1 = Element()
let a2 = Element()
let a = NSArray(objects: a1, a2)
let ma = NSMutableArray(objects: a1, a2)

let ae = a as [Element]        // ok
let mae = ma as [Element]      // error: 'Element' is not identical to 'AnyObject'
let mae2 = ma as NSArray as [Element]  // ok

显然，这是一个错误。