   ///   - key: Object key
   ///   - store: NSPersistentStore where is stored the metadata.
   public func setMetaDataObject(_ object: AnyObject?, with key: String, for store: NSPersistentStore){
-    performChanges (changes: {
+    performChanges {
       guard let psc = self.persistentStoreCoordinator else { fatalError("Persistent Store Coordinator missing.") }
       var md = psc.metadata(for: store)
       md[key] = object
       psc.setMetadata(md, for: store)
-    })
+    }
   }
 
   /// **Mechanica**

  /// **Mechanica**
  ///
  /// Asynchronously performs changes and then saves them or rollbacks if any error occurs.
  public func performChanges(changes: @escaping () -> (), onChangesPerformed: ( (Bool) -> () )? = nil) {
    let queue = OperationQueue.current
    perform {
      changes()
      let result = self.saveOrRollback()
      queue?.addOperation({onChangesPerformed?(result)})
    }
  }


  ///
  /// Synchronously performs changes and then saves them or rollbacks if any error occurs.
  /// - returns: true if the save succeeds, otherwise false.
  @discardableResult
  public func performChangesAndWait(changes: @escaping () -> ()) -> Bool {
    var result = false
    performAndWait {
