 */
 class Migrator_v0_v1: MigratorType {
     
-    internal let persistence: Persistence
+    internal var persistence: Persistence
     required init(persistence: Persistence) {
         self.persistence = persistence
     }


public protocol MigratorType {
    init(persistence: Persistence)
    var persistence: Persistence { get }
    func isMigrationRequired() -> Bool
    func attemptMigration() throws
}

public class CompositeMigrator: MigratorType {
    
    public var persistence: Persistence {
        get {
            preconditionFailure("No persistence here")
        }
        set {
            for var i in self.childMigrators {
                i.persistence = newValue
            }
        }
    }
    
    internal let childMigrators: [MigratorType]
    public required init(persistence: Persistence) {
        self.childMigrators = [
            Migrator_v0_v1(persistence: persistence),
