SwiftでClassを作るときにNSObjectを継承するべき？

どっちを採用するべき？

class Animal {}
// or 
class Animal: NSObject {}

こっちのにしておけばとりあえず間違いないとか、こっちを使うとこんな時に困るとかそういう指針が知りたい。

よさそうな回答

<a href="http://stackoverflow.com/questions/24057525/swift-native-base-class-or-nsobject">Swift native base class or NSObject</a>stackoverflow.com

NSObjectを採用する時
- Objective-Cのクラス
- メソッドを呼ぶ時にobjc_msgSend()を使ってる
- Objective-Cのランタイム時に取得する情報を使ってる時
Nativeクラスでいいとき

Swift classes that are subclasses of NSObject:

are Objective-C classes themselves

use objc_msgSend() for calls to (most of) their methods

provide Objective-C runtime metadata for (most of) their method implementations

Swift classes that are not subclasses of NSObject:

are Objective-C classes, but implement only a handful of methods for NSObject compatibility

do not use objc_msgSend() for calls to their methods (by default)

do not provide Objective-C runtime metadata for their method implementations (by default)

Subclassing NSObject in Swift gets you Objective-C runtime flexibility but also Objective-C performance. Avoiding NSObject can improve performance if you don't need Objective-C's flexibility.

With Xcode 6 beta 6, the dynamic attribute appears. This allows us to instruct Swift that a method should use dynamic dispatch, and will therefore support interception.

public dynamic func foobar() -> AnyObject {}