Swift MCQ: Swift Multiple Choice Questions and Answers

All value types in Swift are **_** under the hood?

What is wrong with this code?

let val = 5.0 + 10

In the function below, what are this and toThat examples of?

func add(this x: Int, toThat y: Int)->{}

Which object allows you access to specify that a block of code runs in a background thread?

What does this code print?

let names = ["Bear", "Tony", "Svante"]
print(names[1]+"Bear")

What is the value of names after this code is executed?

let names = ["Bear", "Joe", "Clark"]
names.map { (s) -> String in
  return s.uppercased()
}

What is the type of this function?

func add(a: Int, b: Int) -> Int { return a+b }

What is this code an example of?

let val = (Double)6

What does this code print to the console?

var userLocation: String = "Home" {
  willSet(newValue) {
  print("About to set userLocation to \(newValue)...")
  }

  didSet {
  if userLocation != oldValue {
  print("userLocation updated with new value!")
  } else {
  print("userLocation already set to that value...")
  }
  }
 }

 userLocation = "Work"

What is wrong with this code?

if let s = String.init("some string") {
  print(s)
}

How do you reference class members from within a class?

Which of these choices is associated with unit testing?

What is true of this code?

let name: String?

How do you declare an optional String?

What is the error in this code?

extension String {
  var firstLetter: Character = "c" {
    didSet {
      print("new value")
    }
  }
}

What is printed to the console when this code is executed?

"t".forEach { (char) in
    print(char)
}

What prints when this code is executed?

let s1 = ["1", "2", "3"]
    .filter { $0 > "0" }
    .sorted { $0 > $1 }
print(s1)

How can you sort this array?

var vals = [1,2,3]

What is the error in this code?

let x = 5
guard x == 5 { return }

What is wrong with this code?

for (key, value) in [1: "one", 2: "two"]{
  print(key, value)
}

How many times this code will be executed? —OR— How many times will this loop be performed?

for i in ["0", "1"]{
  print(i)
}

What will this code print to the console?

var items = ["a":1, "b":2, "c":"test"] as [String: Any]
items["c"] = nil
print(items["c"] as Any)

What is this code an example of?

let val = 5
print("value is: \(val)")

What is the value of val after this code is executed?

let i = 5
let val = i * 6.0

How do you designated a failable initializer?

What describes this line of code?

let val = 5

DispatchQueue.main.async takes a block that will be

What's wrong with this code?

class Person {
  var name: String
  var address: String
}

What is the correct way to call this function?

func myFunc(_ a: Int, b: Int) -> Int {
  return a + b
}

What are the contents of vals after this code is executed?

var vals = [10, 2]
vals.sort { (s1, s2) -> Bool in
  s1 > s2
}

What is the value of oThings after this code is executed?

let nThings: [Any] = [1, "2", "three"]
let oThings = nThings.reduce("") { "\($0)\($1)" }

What data type is this an example of?

let vals = ("val", 1)

What is printed when this code is executed?

let dbl = Double.init("5a")
print(dbl ?? ".asString()")

How many parameters does the initializer for Test have?

struct Test{
  var score: Int
  var date: Date
}

Why is dispatchGroup used in certain situations?

What is the value of y?

let x = ["1", "2"].dropFirst()
let y = x[0]

What is the inferred type of x?

let x = ["a", "b", "c"]

What must a convenience initializer call?

 How many values does vals have after this code is executed?

var vals = Set<String> = ["4", "5", "6"]
vals.insert("5")

What does this code print?

enum Positions : Int {
  case first, second, third, other
}
print (Positions.other.rawValue)

What is wrong with this code?

self.callback = {
  self.attempts += 1
  self.downloadFailed()
}

How would you call a function that throws errors and also returns a value?

What is the base class in this code?

class LSN : MMM {
}

What is the value of test after this code executes?

let vt = (name: "ABC", val: 5)
let test = vt.0

What does this code print?

typealias Thing = [String:Any]
var stuff : Thing
print(type(of:stuff))

In this code, what are wheels and doors examples of?

class Car {
  var wheels: Int = 4
  let doors = 4
}

What is the raw/underlying type of this enum?

enum Direction {
  case north, south, east, west
}

When a function takes a closure as a parameter, when do you want to mark is as escaping?

In the code below, what is width an example of?

class Square{
  var height: Int = 0
  var width : Int {
    return height
  }
}

When is deinit called?

The Codable protocol is **_**?

didSet and willSet are examples of \***\*\_\*\***?

What is wrong with this code?

var x = 5
x = 10.0

What is the value of test in this code?

var test = 1 == 1

How many times will this loop be executed?

for i in 0...100 {
  print(i)
}

What does this code print?

typealias Thing = [String, Any]
var stuff: Thing
print(type(of: stuff))

What can AnyObject represent?

What is the value of t after this code is executed?

let names = ["Larry", "Sven", "Bear"]
let t = names.enumerated().first().offset

How can you avoid a strong reference cycle in a closure?a

Which code snippet correctly creates a typealias closure?

What is the value of y?

var x: Int?
let y = x ?? 5

What is the type of value1 in this code?

let value1 = "\("test".count)"

What prints to the console when executing this code?

let x = try? String.init("test")
print(x)

What is the correct way to add a value to this array?

var strings = [1, 2, 3]