Realmに保存する要素の書き方について

前提・実現したいこと

SwiftでDiaryを応用させたアプリを作っています。
まだ日記の部分を作っている途中なのでRealm活用編
こちらの記事を使って勉強しています。

発生している問題・エラーメッセージ

Realmに保存する要素を書いているコードでエラーが出ます。

Variable used within its own initial value

該当のソースコード

let diary = Diary()ともともと書いていたのですがそれだと
◉Use of unresolved identifier 'Diary'; did you mean 'diary'?
が出てしまいます。
DiaryのファイルはRealmObjectです

 @IBAction func saveButtonPushed(_ sender: UIButton) {

        let realm = try! Realm()
        print(Realm.Configuration.defaultConfiguration.fileURL!)

        let diary = diary() //ここ！
        diary.date = date
        diary.context = contextTextView.text


        try! realm.write {
            realm.add(diary, update: true)
        }

        self.dismiss(animated: true, completion: nil)

    }

DiaryViewController

import UIKit
import RealmSwift

class DiaryViewController: UIViewController {

    @IBOutlet var dateLabel: UILabel!

    @IBOutlet var contextTextView: UITextView!

    var date: String! 

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        dateLabel.text = date

    }


    @IBAction func saveButtonPushed(_ sender: UIButton) {

        let realm = try! Realm()
        print(Realm.Configuration.defaultConfiguration.fileURL!)

        let diary = diary() //error
        diary.date = date
        diary.context = contextTextView.text

        try! realm.write {
            realm.add(diary, update: true)
        }

        self.dismiss(animated: true, completion: nil)

    }

}

Diaryの中身

import Foundation
import RealmSwift

class diary: Object {
    @objc dynamic var date : Date = Date()
    @objc dynamic var context : String = ""
    @objc dynamic var photo: NSData? = nil 

    override static func primaryKey() -> String? {
        return "date"
    }  
}

ViewController

import UIKit
import JBDatePicker

class ViewController: UIViewController, JBDatePickerViewDelegate {

    @IBOutlet var datePicker: JBDatePickerView!
    @IBOutlet var writebutton: UIButton!

    var date: String!

    lazy var dateFormatter: DateFormatter = {
        var formatter = DateFormatter()
        formatter.timeStyle = .none
        formatter.dateStyle = .medium
        return formatter
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        datePicker.updateLayout()
    }

    func didSelectDay(_ dayView: JBDatePickerDayView) { //JBDatePickerのDelegateメソッド

        print("date selected: \(dateFormatter.string(from: dayView.date!))")
         date = dateFormatter.string(from: dayView.date!)

    }

    @IBAction func writeButtonPushed(_ sender: UIButton) {
         self.performSegue(withIdentifier: "toDiary", sender: nil)
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) { 
        if (segue.identifier == "toDiary") {

            let diaryView = segue.destination as! DiaryViewController
            diaryView.date = self.date
        }
    }


}