They are both representing the nonowning relationship.
But the diffrence is:
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The new CaseIterable protocol gives your Enum new ability to generate an array of all cases in an enum.

The error message when you reused an AVCapturePhotoSettings object is -[AVCapturePhotoOutput capturePhotoWithSettings:delegate:] Settings may not be re-used'.

直接跳到Swift语言吧。Swift很快很安全，而且就我的感受来说，写Swift有一种写脚本语言的快感。但是Swift还有很多路要走，现在最感到头疼的就是和ObjC的混编吧。

更多数据结构

数据结构

AVPlayer

AVFoundation provides a controller class AVPlayer to play timed audio-visual media. The AVPlayer can handle playback of local, progressively downloaded and streamed media conforming HLS protocol.