Extension of a generic Objective-C class cannot access the class's generic parameters at runtime

[davelee (David Lawrence)]

I'm attempting to extend NSFetchRequest to conform to a more abstract protocol, as shown below. But doing so results in the error "Extension of a generic Objective-C class cannot access the class's generic parameters at runtime".

I realize that the Core Data is an Objective-C library, and that NSFetchRequest is generic, but I don't understand how to work around this error. I'm running Xcode 10.2 & Swift 4.2.

import Foundation
import CoreData

protocol Request {
    var from: String? {get}
}

extension NSFetchRequest: Request {
    var from: String? {
        get {
            return self.entityName
        }
    }
}