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

DiaryViewController
1 @IBAction func saveButtonPushed(_ sender: UIButton) {
2
3        let realm = try! Realm()
4        print(Realm.Configuration.defaultConfiguration.fileURL!)
5      
6        let diary = diary() //ここ！
7        diary.date = date
8        diary.context = contextTextView.text
9
10       
11        try! realm.write {
12            realm.add(diary, update: true)
13        }
14
15        self.dismiss(animated: true, completion: nil)
16      
17    }
18

DiaryViewController

swift
1import UIKit
2import RealmSwift
3
4class DiaryViewController: UIViewController {
5    
6    @IBOutlet var dateLabel: UILabel!
7
8    @IBOutlet var contextTextView: UITextView!
9    
10    var date: String! 
11    
12    override func viewDidLoad() {
13        super.viewDidLoad()
14
15        // Do any additional setup after loading the view.
16    }
17    
18    override func didReceiveMemoryWarning() {
19        super.didReceiveMemoryWarning()
20        // Dispose of any resources that can be recreated.
21    }
22    
23    override func viewWillAppear(_ animated: Bool) {
24        super.viewWillAppear(animated)
25        
26        dateLabel.text = date
27        
28    }
29
30    
31    @IBAction func saveButtonPushed(_ sender: UIButton) {
32
33        let realm = try! Realm()
34        print(Realm.Configuration.defaultConfiguration.fileURL!)
35        
36        let diary = diary() //error
37        diary.date = date
38        diary.context = contextTextView.text
39
40        try! realm.write {
41            realm.add(diary, update: true)
42        }
43
44        self.dismiss(animated: true, completion: nil)
45      
46    }
47    
48}

Diaryの中身

swift
1import Foundation
2import RealmSwift
3
4class diary: Object {
5    @objc dynamic var date : Date = Date()
6    @objc dynamic var context : String = ""
7    @objc dynamic var photo: NSData? = nil 
8    
9    override static func primaryKey() -> String? {
10        return "date"
11    }  
12}

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
        }
    }
    
    
}