Swift Fundamentals

Question 1

What’s the difference between mutable and immutable ?

Answer 1

A mutable object allows for change. An immutable object does not allow for changes.

Question 2

What is a property observer?

Answer 2

A property observer listens for changes on an object. One can listen for changes when the object is about to get set and when the object actually got set.

Question 3

What is a computed property ?

Answer 3

A computed property returns the value of a block of calculated logic.

Question 4

What are higher order functions?

Answer 4

A function that takes another function as an argument or returns a function is said to be a higher order function. This is the fundamental pillar of functional programming.

Question 5

What is recursion?

Answer 5

A function that calls itself. The two main parts of a recursive function is the base case and the recursive call.

Question 6

What are access control / modifiers and give three examples?

Answer 6

Access control provide varied level of access to parts of the code of an object from another source object.

private
public
internal

Question 7

Name three built-in protocols in Swift and their use cases?

Answer 7

Hashable. Types conforming to Hashable will be guaranteed to be unique.

CaseIterable. Enums conforming to CaseIterable will make all their cases available and iterable.

CustomStringConvertible. Conforming to CustomStringConvertible allows a type to override the description property on an object and return a custom String.

Question 8

What’s the benefit of an inout function?

Answer 8

To be able to mutate via referencing the data outside the scope of a function.

Question 9

What is an optional ?

Answer 9

In Swift an optional is a type used to indicate that an object can or not have a value.

Question 10

What are Closures ?

Answer 10

Closures are anonymous functions (functions without a name) that capture references to values in their surrounding context. This is one of the subtle differences between functions and closures. Please note however that nested functions also capture their surrounding values.

Question 11

What is GCD?

Answer 11

Grand central dispatch is the library that iOS uses to handle concurrency.

Question 12

Name the types of loops available in Swift ?

Answer 12

while, for-in, and repeat-while

Question 13

If using a Command-line macOS application what’s the function used for taking user input ?

Answer 13

For user input or STDIN when working in a command-line application we use readLine().

Question 14

What is the restriction on a dictionary ?

Answer 14

The keys need to conform to Hashable.

Question 15

What is Object Oriented Programming ?

Answer 15

A paradigm used in programming to represent objects and encapsulate their properties and functions.

// Parent class
class Person {
  var name: String
  var age: Int

init(name: String, age: Int) {
self.name = name
self.age = age
}

  func info() {
    print("Hi, my name is \(name)")
  }
}

// Fellow inherits from the Person class
// Subclass
class Fellow: Person {}

let fellow = Fellow(name: "Xavier Li", age: 23)
fellow.info() // Hi, my name is Xavier Li

Question 16

Name three principles of OOP ?

Answer 16

Inheritance, Encapsulation and Polymorphism.

Encapsulation means that objects keep their state information private. Rather than directly manipulating an object’s data, other objects send requests to the object, in the form of messages, some of which the object may respond to by altering its internal state.

Polymorphism means that objects of different classes can be used interchangeably. This is especially important, as it allows you to hook up classes at a later date in ways you didn’t necessarily foresee when those classes were first designed.

Inheritance means that objects of one class can derive part of their behavior from another (base or parent) class. Some object-oriented languages (C++, for example, but not Swift) allow multiple inheritance, where objects of one class can derive part or all of their behavior from multiple independent base classes.

Question 17

What is Protocol Oriented Programming ?

Answer 17

In Swift this is a paradigm used to describe the blueprint of functions and properties that a conforming object needs to adhere to.

protocol Vehicle {
  var wheels: Int { get }
  var color: UIColor { set get }
  func drive(speed: Int)
}

struct Bike: Vehicle {
  let wheels = 2
  var color = UIColor.systemGray

  func drive(speed: Int) {
    print("current speed is \(speed)")
  }
}

let bike = Bike()

bike.drive(speed: 23) // current speed is 23

Question 18

What is dependency injection?

Answer 18

Dependency Injection is used to pass all required properties and data over to an object. This is better done through the use on an initializer as the object can fully encapsulate its properties.

Question 19

What framework is used for writing Unit Test in iOS ?

Answer 19

XCTest

Question 20

What is a Singleton?

Answer 20

A singleton is making use of one instance of a class throughout the life of the launch of an application. One of the main pillars of singleton is the use of marking initializers private so accidental creation of multiple instances is prohibited.

Singletons are used throughout iOS in places like UserDefaults.standard, FileManager.default and UIApplication.shared.

Question 21

Is URLSession part of Foundation or UIKit?

Answer 21

URLSession is part of the Foundation framework.

Question 22

What’s the difference between a compile time error and a runtime error?

Answer 22

Compile time errors occurs during the writing phase of your code. Runtime errors occurs during the launch and actual use of the application.

Question 23

Is Index out of range error on an array an compile-time error or a runtime error?

Answer 23

Index out of range is a runtime error.

Question 24

What’s the difference between Structs and Classes?

Answer 24

Structs are passed-by value (value-types) meaning copies of the objects are passed around thereby making the objects immutable by default. Classes are reference types and their state is easily mutated as objects that have the same reference can make changes at will.

Question 25

What is Type Annotation?

Answer 25

Type annotation is explicitly marking the data type of a variable or constant upon initialization.

Question 26

What is Type Inference?

Answer 26

Type inference is allowing the Swift compiler to determine the data type.

Question 27

Is NSString a class or a struct?

Answer 27

NSString is an objective-c API and is a class. With interoperability we can easily bridge between Swift String and NSString.

Question 28

What’s the difference between frames and bounds?

Answer 28

The frame represents an object’s superview and it’s relationship in the coordinate space, whereas the bounds represents the objects own size and location.