let naamVariabele = 5 

class Cat {
	func sayHello() -> String {
		return "Meow!"
	}
}

func schrodingersCat() -> Cat? {
	// Open the box!
	let cat = [0, 1].randomElement()
	
	if cat == 1 {
		return Cat() 
	}
	else {
		return nil
	}
}

if let kitty = schrodingersCat() {
	print(kitty.sayHello())
}
else {
	print("Poor kitty.")
}

If You make a network call and do a debugPrint(response) instead of print(response), you will get a lot more valuable information. See the below example code:

Sample Code : Using iTunes Search Api
    let urlReq = URLRequest(url: URL(string: "https://itunes.apple.com/search?term=jack+johnson&limit=1")!)

    Alamofire.request(urlReq).responseJSON { (data) in
        print(data)
        print("\n\n\n\n\n\n\n\n\n")
        debugPrint(data)
    }
    
Console Output (Removing some of the response fields)

/////////////////////////For print//////////////////////////////
SUCCESS: {
    resultCount = 1;
    results =     (
                {
            artistId = 909253;
            artistName = "Jack Johnson";
            artistViewUrl = "https://itunes.apple.com/us/artist/jack-johnson/id909253?uo=4";
        }
    );
}
////////////////////// For debugPrint //////////////////////////////////////
[Request]: GET https://itunes.apple.com/search?term=jack+johnson&limit=1
[Response]: <NSHTTPURLResponse: 0x610000223860> { URL: https://itunes.apple.com/search?term=jack+johnson&limit=1 } { status code: 200, headers {
    "Access-Control-Allow-Origin" = "*";
    "Cache-Control" = "max-age=86345";
    Connection = "keep-alive";
    "Content-Disposition" = "attachment; filename=1.txt";
    "Content-Length" = 1783;
    "Content-Type" = "text/javascript; charset=utf-8";
    Date = "Sat, 23 Sep 2017 14:29:11 GMT";
    "Strict-Transport-Security" = "max-age=31536000";
    Vary = "Accept-Encoding";
    "X-Apple-Partner" = "origin.0";
    "X-Cache" = "TCP_MISS from a23-76-156-143.deploy.akamaitechnologies.com (AkamaiGHost/9.1.0.4-20866905) (-)";
    "X-Cache-Remote" = "TCP_MISS from a23-45-232-92.deploy.akamaitechnologies.com (AkamaiGHost/9.1.0.4-20866905) (-)";
    "X-True-Cache-Key" = "/L/itunes.apple.com/search ci2=limit=1&term=jack+johnson__";
    "apple-originating-system" = MZStoreServices;
    "apple-seq" = 0;
    "apple-timing-app" = "86 ms";
    "apple-tk" = false;
    "x-apple-application-instance" = 1000492;
    "x-apple-application-site" = NWK;
    "x-apple-jingle-correlation-key" = VEF3J3UWCHKUSGPHDZRI6RB2QY;
    "x-apple-orig-url" = "https://itunes.apple.com/search?term=jack+johnson&limit=1";
    "x-apple-request-uuid" = "a90bb4ee-9611-d549-19e7-1e628f443a86";
    "x-apple-translated-wo-url" = "/WebObjects/MZStoreServices.woa/ws/wsSearch?term=jack+johnson&limit=1&urlDesc=";
    "x-content-type-options" = nosniff;
    "x-webobjects-loadaverage" = 0;
} }
[Data]: 1783 bytes
[Result]: SUCCESS: {
    resultCount = 1;
    results =     (
                {
            artistId = 909253;
            artistName = "Jack Johnson";
            artistViewUrl = "https://itunes.apple.com/us/artist/jack-johnson/id909253?uo=4";
        }
    );
}

[Timeline]: Timeline: 

{
  "Request Start Time": 527869893.013,
  "Initial Response Time": 527869893.033,
  "Request Completed Time": 527869893.034,
  "Serialization Completed Time": 527869893.035,
  "Latency": 0.020secs,
  "Request Duration": 0.021secs,
  "Serialization Duration": 0.001secs,
  "Total Duration": 0.021secs
}

1.) using toggle function
var isVisible = true
print(isVisible.toggle())  // false

2.) using ! is the "logical not" operator:
var x = true
x = !x
print(x) // false

class Singleton {
    var name = "sumit"
    static let shared = Singleton()
    
    private init() {
        // don't forget to make this private
    }
}
let singleton = Singleton.shared
let A = Singleton.shared
let B = Singleton.shared
print(A.name)
print(B.name)

A.name = "Ankit"
print(A.name)
print(B.name)

arr = Array(Set(arr))

arr = Array(Set(arr))

1. Struct
// Importance of struct: Sensor is struct so that appending in array can be done with value not by reference
struct MotionSensor {
    var dateFormatter = DateFormatter() // to convert date into string
    init(newFormatter: DateFormatter)
    {
        self.dateFormatter = newFormatter
    }
    
    func toString() -> String
    {
    }
  }
2. Class
class LocationSensorData
{
    var arr = [LocationSensor]()
    var i = 0
    init()
    {
        //iniitalization
        
    }
    
    func toString() -> String{
        var myString = ""
        for sensor1 in arr
        {
            myString += sensor1.toString() + "\n"
            //            print("\(self.i)  : \(sensor1.actionType!)")
            //            self.i = self.i + 1
            
        }
        
        return myString
    }
    
}

3. NSArray,NSImmputable Array
In contrast, a Foundation NSArray is immutable by default. If you want to add, 
remove or modify items after creating the array, you must use the mutable variant class NSMutableArray
An NSArray is heterogeneous, meaning it can contain Cocoa objects of different types. Swift arrays are homogeneous, meaning that each Array is guaranteed to contain only one type of object
However, you can still define a single Swift Array so it stores various types of Cocoa objects by specifying that the one type is AnyObject, since every Cocoa type is also a subtype of this.


4. Swift array
Swift arrays are immutable if you define them as constants with let, and mutable 
if you define them as variables with var.

var arr = [34,534,634,345,234]
let indexes = [0,3,4]
arr = indexes.compactMap{ arr[$0] } // [34, 345, 234]

extension Array where Element == Int {
    func median() -> Double? {
        guard count > 0  else { return nil }

        let sortedArray = self.sorted()
        if count % 2 != 0 {
            return Double(sortedArray[count/2])
        } else {
            return Double(sortedArray[count/2] + sortedArray[count/2 - 1]) / 2.0
        }
    }
}

let arr = [1,2,3,4,5,6,7,8,9]
if let median = arr.median() {
    // do something
}