Xcode 6.3 Crashes when navigating from storyboard to other Swift 1.2 file

Question

I installed Xcode 6.3 which includes support for Swift 1.2. It turned up a ton of error messages, which are mostly casting issues.

I navigated to the storyboard, an

Answer 1

A temporary solution:

By opening a "New Window" (same project).

One for the code, one for the storyboard or reduce first, work freely with second window.

You can keep your @IBDesignables

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EDIT : Bug fixed -> Update Xcode 6.3.1