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passKit/Extensions/UITextFieldExtension.swift

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+//
+//  UITextFieldExtension.swift
+//  pass
+//
+//  Created by Yishi Lin on 5/4/17.
+//  Copyright © 2017 Yishi Lin. All rights reserved.
+//
+
+import Foundation
+import UIKit
+
+private var kAssociationKeyNextField: UInt8 = 0
+
+extension UITextField {
+    @IBOutlet var nextField: UITextField? {
+        get {
+            return objc_getAssociatedObject(self, &kAssociationKeyNextField) as? UITextField
+        }
+        set(newField) {
+            objc_setAssociatedObject(self, &kAssociationKeyNextField, newField, .OBJC_ASSOCIATION_RETAIN)
+        }
+    }
+}