昨天发布的最新Xcode版本9.4Beta增加了对ClassKit的支持

ClassKit 开发文档

About Xcode 9.4 beta

Supported Configurations

Xcode 9.4 beta requires a Mac running macOS 10.13.2 or later.

SDK Versions

Xcode 9.4 beta includes SDKs for iOS 11.4, watchOS 4.3, macOS 10.13.4, and tvOS 11.4.

9.4 版本已知的问题，不支持构建运行 tvOS 11.3

Xcode 9.4 beta does not support building and running on devices running tvOS 11.3. (39042488)

9.4版本中修复的问题

Asset Catalog
Resolved an issue that could cause progress to get stuck while editing AR assets
in an Asset Catalog. (38393995)
Resolved an issue that could cause a crash when dragging a .gif image into a
Sticker Pack in an Asset Catalog. (38820366)
Instruments
Resolved an issue where loading a saved trace could result in an empty Symbols…
panel. (38813311)

以及Swift中的一些问题

Resolved in Xcode 9.4 beta – Swift
Compiler
Swift Compiler
Swift now correctly handles the case where protocol methods or base class
methods defined in Objective-C claim to take non-null arguments of type id in their
headers, but get invoked with nil values at runtime

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