Swift:无法将类型 'UnsafeMutablePointer' 的值转换为预期的参数类型 'UnsafeMutablePointer'

Question

更新到 Swift 3 后，我的代码出现了一些问题。我在转换之前有这段代码:

extension NSData {
  func castToCPointer<T>() -> T {
    let mem = UnsafeMutablePointer<T>.alloc(sizeof(T.Type))
    self.getBytes(mem, length: sizeof(T.Type))
    return mem.move()
  }
}

然后我将其转换为此代码，在第 3 行出现错误

... Cannot convert value of type 'UnsafeMutablePointer' to expected argument type 'UnsafeMutablePointer'

extension Data {
  func castToCPointer<T>() -> T{
    let mem = UnsafeMutablePointer<T>.allocate(capacity: MemoryLayout<T.Type>.size)
    self.copyBytes(to: mem, count: MemoryLayout<T.Type>.size)
    //self.copyBytes(to: mem, count: MemoryLayout<T.Type>.size)
    return mem.move()
  }
}

有谁知道如何摆脱这个？

Answer 1

copyBytes 需要一个 UnsafeMutableBufferPointer 作为参数:

extension Data {
    func castToCPointer<T>() -> T {
        let mem = UnsafeMutablePointer<T>.allocate(capacity: 1)
        _ = self.copyBytes(to: UnsafeMutableBufferPointer(start: mem, count: 1))
        return mem.move()
    }
}

(allocate() 将“items”的数量作为参数，而不是字节。)

但是注意你的方法会泄漏内存，分配的内存被取消初始化(使用 move())但也必须是释放:

extension Data {
    func castToCPointer<T>() -> T {
        let mem = UnsafeMutablePointer<T>.allocate(capacity: 1)
        _ = self.copyBytes(to: UnsafeMutableBufferPointer(start: mem, count: 1))
        let val =  mem.move()
        mem.deallocate(capacity: 1)
        return val
    }
}

一个更简单的解决方案是(来自 round trip Swift number types to/from Data ):

extension Data {
    func castToCPointer<T>() -> T {
        return self.withUnsafeBytes { $0.pointee }
    }
}