See Apple release note

Notes from IBInspectable / IBDesignable

user-defined runtime attributes: allows updating attribute value in Xcode

IBInspectable: easlier editable in Xcode

Can add inspectable property to existing classes via extension.

IBDesignable: WYSIWYG.

Use prepareForInterfaceBuilder() to provide dummy data at design time. It’s not run in shipping code.

A clusure that is

• passed in to a function as parameter
• called after the function has returned

Closures are non-escaping by default in Swift 3+.

Use @escaping to mark it as escaping.

• api calls
• disk I/O
• data preparation