Swift 1.2 将 [AnyObject?] 转换为 [AnyObject]

Question

如果你看一下这个函数:

typealias JSONDictionary = [String: AnyObject]

private func allIdentifiersInJson(json: [JSONDictionary], key: String?) -> [AnyObject] {
        if let identifier = key {
            let identifiers = json.map{ $0[identifier] } //this returns [AnyObject?]
            return identifiers as? [AnyObject] ?? [] // this crashes the compiler in Release with Optimizations
        }
        return []
    }

如何将 [AnyObject?] 转换为 [AnyObject]

在启用优化的 Release 配置中，我在编译期间遇到此错误:

Bitcast requires both operands to be pointer or neither
  %548 = bitcast i64 %547 to %objc_object*, !dbg !10033
LLVM ERROR: Broken function found, compilation aborted!

Answer 1

一种方法是使用 flatMap:

let l: [AnyObject?] = [1, 2, 3, 4, 5, 6, nil, 7]
let m = l.flatMap { $0 } // Returns [1, 2, 3, 4, 5, 6, 7] as [AnyObject]

(仅在 Swift 2 中测试过)