gistfile1.swift

extension NSManagedObject {
    class func createEntity<T: NSManagedObject>(context: NSManagedObjectContext) -> T {
        return NSEntityDescription.insertNewObjectForEntityForName(NSStringFromClass(T), inManagedObjectContext: context) as! T
    }
}

class Customer: NSManagedObject {
    @NSManaged var id: NSNumber
}

Then call it:

let customer = Customer.createEntity(managedObjectContext)