Property cannot be marked @nsmanaged because its type cannot be represented in objective-c

Answer: The error message “property cannot be marked @nsmanaged because its type cannot be represented in objective-c” occurs when a property cannot be marked with the `@NSManaged` attribute in Objective-C code.

In Objective-C, properties that use the `@NSManaged` attribute must have a type that can be represented in Objective-C. This is because `@NSManaged` properties are used for Core Data integration, which requires compatibility with Objective-C.

For example, if you have a property in Swift with a type that cannot be represented in Objective-C, such as a Swift specific type or a protocol, you will encounter this error:

@NSManaged var myProperty: MyProtocol
  

In this case, you need to choose a type that can be represented in Objective-C for the property. Core Data supports a set of predefined types that can be represented in Objective-C, such as `NSString`, `NSNumber`, `NSDate`, etc.

If you need to store a Swift specific type in Core Data, you can consider transforming it into a compatible type before saving it to the Core Data store. For example, you might transform a custom struct into an `NSData` object.

Here is an example of transforming a custom struct into an `NSData` object and saving it as a binary attribute in Core Data:

@NSManaged var myPropertyData: NSData
  
  var myProperty: MyStruct {
      get {
          guard let data = myPropertyData else {
              return MyStruct()
          }
          
          return NSKeyedUnarchiver.unarchiveObjectWithData(data) as? MyStruct ?? MyStruct()
      }
      
      set {
          myPropertyData = NSKeyedArchiver.archivedDataWithRootObject(newValue)
      }
  }
  

In this example, the actual property that is marked as `@NSManaged` is `myPropertyData`, which is an `NSData` type that can be represented in Objective-C. The `myProperty` computed property is used to provide a Swift specific interface to access and modify the `MyStruct` value.

By properly transforming the property into a compatible type, you can still integrate it with Core Data even if the original type cannot be represented in Objective-C.