array_copy_semantics_workaround.swift

extension Array {
    var unsafePointerToElements: UnsafePointer<T> {
        return self.withUnsafePointerToElements { return $0 }
    }
    subscript (index: Int) -> T {
        get {
            let ptr = self.unsafePointerToElements
            return ptr[index]
        }
        set(rhs) {
            self.unshare()
            let ptr = self.unsafePointerToElements
            if (ptr) {
                ptr[index] = rhs
            }
        }
    }
}

var a1: Array<Int> = [40, 41]
var a2 = a1
a2[1] = 42
println(a1) // [40, 41]
println(a2) // [40, 42]