Swift 中的数组是由结构体实现的：

struct Array<T> : MutableCollection, Sliceable {
    typealias Element = T
    var startIndex: Int { get }
    var endIndex: Int { get }
    subscript (index: Int) -> T
    func generate() -> IndexingGenerator<T[]>
    typealias SliceType = Slice<T>
    subscript (subRange: Range<Int>) -> Slice<T>
    init(_ buffer: ArrayBuffer<T>)
}

而数组的恒等 === 在文档中是这么说的：

Check whether two arrays or subarrays share the same storage and elements by comparing them with the identity operators (=== and !==).

数组的恒等 === 判断即判断两个数组所指向的元素存储区是否相同。

但 XCode 6 Beta 测试下来，结果大为迥异:

var a = [1, 2, 3]
var b = a
var c = a

println("a === a: \(a === a), b === c: \(b === c)");

a === a: false, b === c: false