Closure(Best One)

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let firstAction = UIAlertAction(title: &lt;#T##String?#&gt;, style: .default, handler: &lt;#T##((UIAlertAction) -&gt; Void)?##((UIAlertAction) -&gt; Void)?##(UIAlertAction) -&gt; Void#&gt;)
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alertController.addAction(cancelAction)
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@IBAction func doSomething()
@IBAction func doSomething(sender: UIButton)
@IBAction func doSomething(sender: UIButton, forEvent event: UIEvent)

[[NSProcessInfo processInfo] operatingSystemVersion]

import 'package:flutter/material.dart';

void main() {
  runApp(
    new MaterialApp(
      title: 'Hello World App',
      home: new myApp(),
    )
  );
}

class myApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Hello World App'),
      ),
      body: new Center(
        child: new Text(
          'Hello, world!'
        ),
      ),
    );
  }
}

override func viewDidLoad() {
    super.viewDidLoad()
    // Swift block syntax (iOS 10+)
    let timer = Timer(timeInterval: 0.4, repeats: true) { _ in print("Done!") }
    // Swift >=3 selector syntax
    let timer = Timer.scheduledTimer(timeInterval: 0.4, target: self, selector: #selector(self.update), userInfo: nil, repeats: true)
    // Swift 2.2 selector syntax
    let timer = NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: #selector(MyClass.update), userInfo: nil, repeats: true)
    // Swift <2.2 selector syntax
    let timer = NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: "update", userInfo: nil, repeats: true)
}

// must be internal or public. 
@objc func update() {
    // Something cool
}

// calling 
    getProfileMode { (mode) in
            print("Mode : ", mode)
        }

func getProfileMode(completion: @escaping (String) -> Void) {
           // write firestore code here
            completion("true")
        }

// calling      
UpdateProfileData(dataToUpdate) { (isUpdated) in
            if isUpdated {
                self.aboutTableView.reloadData()
                print("updatedd")
            }
        }

func UpdateProfileData (_ dateToUpdate: [String: Any], completionHandler:@escaping (_ success:Bool) -> Void) {
        
        SVProgressHUD.show()
        let User = Auth.auth().currentUser
        guard let user = User else {
            print("Error45")
            SVProgressHUD.dismiss()
            return
        }
        let db = Firestore.firestore()
        db.collection("Users").document(user.uid).setData(dateToUpdate, merge: true) { (error) in
            if error != nil {
                print("Error99")
                SVProgressHUD.dismiss()
                return
            }
            print("updated")
            completionHandler(true)
            SVProgressHUD.dismiss()
        }
    }

// calling    
        StrutName.updateDocument("Users", "", dataToUpdate) { (isUpdated) in
            if isUpdated {
                    print("Success")
            } else {
                print("Found Error While Updating")
            }
        }

    public static func updateDocument (_ collectionName: String, _ documentId : String, _ dataToUpdate: [String: Any], completionHandler:@escaping (_ success:Bool) -> Void) {
        
        var documentID = ""
        
        SVProgressHUD.show()
        let User = Auth.auth().currentUser
        guard let user = User else {
            SVProgressHUD.dismiss()
            completionHandler(false)
            return
        }
        
        if documentId == "" {
            documentID = user.uid
        } else {
            documentID = documentId
        }
        
        let db = Firestore.firestore()
        db.collection(collectionName).document(documentID).setData(dataToUpdate, merge: true) { (error) in
            
            if error != nil {
                completionHandler(false)
                SVProgressHUD.dismiss()
                return
            }
            print("updated321")
            completionHandler(true)
            SVProgressHUD.dismiss()
        }
    }

   
 FireStore.getDocument("Users", "") { (document, gotDocument) in
    
            if gotDocument {
                print("Success")
            } else {
                print("Error while getting Document")
            }
        }

    public static func getDocument(_ collectionName: String, _ documentId : String, completion: @escaping(_ documentSnapShot : DocumentSnapshot,_ success : Bool) -> Void) {
        
            SVProgressHUD.show()
            let User = Auth.auth().currentUser
            guard let user = User else {
                SVProgressHUD.dismiss()
                return
            }
     
        var docID = ""
        if documentId == "" {
            docID = user.uid
        } else {
            docID = documentId
        }

            let db = Firestore.firestore()
            db.collection(collectionName).document(docID).getDocument { (document, error) in
                
                if error != nil {
                    print("Error :", error as Any)
                    SVProgressHUD.dismiss()
                    return
                }
                
                
                guard let document = document else {
                    print("Error While Getting Document")
                    SVProgressHUD.dismiss()
                    return
                }
                completion(document, true)
            }
    }

   
 StructureName.getDocument("Users", "") { (document, gotDocument) in
    
            if gotDocument {
                print("Success")
            } else {
                print("Error while getting Document")
            }
        }

    public static func getDocument(_ collectionName: String, _ documentId : String, completion: @escaping(_ documentSnapShot : DocumentSnapshot,_ success : Bool) -> Void) {
        
            SVProgressHUD.show()
            let User = Auth.auth().currentUser
            guard let user = User else {
                SVProgressHUD.dismiss()
                return
            }
     
        var docID = ""
        if documentId == "" {
            docID = user.uid
        } else {
            docID = documentId
        }

            let db = Firestore.firestore()
        db.collection(collectionName).document(docID).addSnapshotListener { (document, error) in
                if error != nil {
                    print("Error :", error as Any)
                    SVProgressHUD.dismiss()
                    return
                }
                
                guard let document = document else {
                    print("Error While Getting Document")
                    SVProgressHUD.dismiss()
                    return
                }
                completion(document, true)
            }
    }

// Preferred status bar style lightContent to use on dark background.
// Swift 3
override var preferredStatusBarStyle: UIStatusBarStyle {
    return .lightContent
}

// MARK: - Properties

// MARK: - IBOutlets

// MARK: - Life cycle

// MARK: - Set up

// MARK: - IBActions

// MARK: - Navigation

// MARK: - Network Manager calls

// MARK: - Extensions

import UIKit

extension UITableView {
    
    func dequeueReusableCell<T: UITableViewCell>() -> T {
        return dequeueReusableCell(withIdentifier: NSStringFromClass(T.self)) as! T
    }
}

//using: let cell: ExampleTableViewCell = tableView.dequeueReusableCell()

#include <iostream>
#include "unordered_set"
#include "basicActions.h"
using namespace std;

void createLoop(Node *head)
{
    Node *p = head;

    while (p->next != nullptr)
    {
        p = p->next;
    }
    p->next = head;
    return;
}

bool detectLoop(Node *head)
{
    unordered_set<Node *> s;
    Node *p = head;

    while (p != nullptr)
    {
        if (s.find(p) != s.end())
            return true;

        s.insert(p);
        p = p->next;
    }
    return false;
}

int main()
{
    Node *head = nullptr;
    insertAtEnd(head, 1);
    insertAtEnd(head, 2);
    insertAtEnd(head, 3);
    insertAtEnd(head, 4);
    insertAtEnd(head, 5);

    createLoop(head);

    detectLoop(head) ? cout << "Loop Detected.." << '\n' : cout << "No Loop Detected.." << '\n';
}

#include <iostream>
using namespace std;

struct hashing
{
    int value;
    int key;
};


void put(int value, hashing hash[],int n) {
    hash[value % n].value = value;
    hash[value % n].key = (value % n);
}

int get(int key, hashing hash[]) {
    return hash[key].value;
}

int main()
{
    int n;
    
    struct hashing hash[n];
    cin >> n;
    for (int t=0;t<n;t++) {
        put(t+1,hash,n);
        cout << "Inserted : " << (t+1) << endl;
    }
    int temp;
    cin >> temp;
    cout << get(temp,hash) << endl;
}