Blog post / Dynamic Type - Extending Optional when the wrapped value is of type UIFont, so we can return the custom font object or precondition failure

UIFont+Optional.swift

extension Optional where Wrapped == UIFont {
    
    var unwrapped: Wrapped {
        switch self {
        case .some(let font): return font
        case .none:
            preconditionFailure("""
                Could not load font from available fonts:
                \(UIFont.familyNames.joined(separator: ", "))
            """)
        }
    }
}