How to declare a Core Data transient property in Swift

TL;DR: use @objc
 
Source: the 5th comment to the 2nd answer to this Stack Overflow question.
 
Sample code:

@objc public var firstInitial: String {
        
    willAccessValue(forKey: "firstInitial")
    let name = self.name
    didAccessValue(forKey: "firstInitial")
        
    guard let groupName = name,
        let initial = groupName.first else { 
            return ""
    }
        
    return String(initial).uppercased()
}

(and yes I know there are many different ways I could compute the first initial of a string.)