简单的 IOS 语句理解

最近在学ios 有两句代码没能理解 求大神解答一下

+ (instancetype)new __attribute__

((unavailable("[+new] is not allowed, use [+cameraWithRootView:andCaptureView:]")));

• (instancetype) init attribute ((unavailable("[-init] is not allowed, use [+cameraWithRootView:andCaptureView:]")));

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