ios - 关于swift中源码的一点疑问

Question

我在查看Xcode中查看swift的源码，遇到几个问题：
如下：UITableViewController继承了UIViewController

@available(iOS 2.0, *)
public class UITableViewController : UIViewController, UITableViewDelegate, UITableViewDataSource {
    
    public init(style: UITableViewStyle)
    public init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?)
    public init?(coder aDecoder: NSCoder)
    
    public var tableView: UITableView!
    @available(iOS 3.2, *)
    public var clearsSelectionOnViewWillAppear: Bool // defaults to YES. If YES, any selection is cleared in viewWillAppear:
    
    @available(iOS 6.0, *)
    public var refreshControl: UIRefreshControl?
}

然后我点击到UIViewController中看了下，它也是个class类：

@available(iOS 2.0, *)
public class UIViewController : UIResponder, NSCoding, UIAppearanceContainer, UITraitEnvironment, UIContentContainer, UIFocusEnvironment {
...省略一些代码

@available(iOS 6.0, *)
    public func canPerformUnwindSegueAction(action: Selector, fromViewController: UIViewController, withSender sender: AnyObject) -> Bool

@available(iOS 9.0, *)
    public func allowedChildViewControllersForUnwindingFromSource(source: UIStoryboardUnwindSegueSource) -> [UIViewController]
...省略一些代码

里面有上面那样子没有方法体的方法声明，我理解的swift不是只有在协议中才可以定义方法，而没有方法体吗？而UIViewController是个class类，为什么里面的方法也可以没有方法体呢？

Answer 1

I think what you see is like the header file in obj c before. It is just an interface definition, just like a document, not an actual class.