Swift Interview Questions

Swift Interview Questions

  • PD Singh
  • 31st Dec, 2020
Ios Swift is a dialect that is extremely for secure coding since it effortlessly wipes out all untrustworthy code classes and guarantees secure coding condition to create a steady arrangement. Swift is a robust and specially dialect. It makes a compiler blunder i.e. AS when you compose an uncouth code. Besides, it likewise decreases the time and assets exhausted on bug settling. In this way lessens code length. Moreover, Swift applications are effortlessly good with the largely recent OS X Yosemite, iOS adaptations, and OS X Mavericks. Today Swift has turned out to be a standout in the middle of other stages, which is recognized by decreasing the measure of coding, required intended for monotonous articulations and sequenced administration.

Swift Interview Questions

1) What is iOS Swift?

IOS Swift is a general-purpose, multi-paradigm, compiled programming language developed by Apple Inc. For iOS, iPadOS, macOS, watchOS, tvOS, Linux, and z/OS. Swift is designed to work with Apple's Cocoa and Cocoa Touch frameworks and the large body of existing Objective-C code written for Apple products.

2) Enlist major advantages of Swift Programming Language?

Some of the advantages of Swift programming languages are mentioned below:-  

  • Rapid development process.
  • Easier to scale the product and the team.
  • Improved safety and performance.
  • Decreased memory footprint.
  • Interoperability with Objective-C.
  • Automatic memory management.
  • Full stack potential and cross-device support.

3) List major features of Swift?

Some major features of swift are mentioned below:-  

  • Closures unified with function pointers.
  • Tuples and multiple return values.
  • Fast and concise iteration over a range or collection.
  • Structs that support methods, extensions, and protocols.
  • Functional programming patterns, e.g., map and filter.

4) List major tools required to develop an iOS application?

Some of the tools required to develop an iOS application are mentioned below:-  

  • Xcode:- It is the most amazing tool for building iconic apps for all Apple platforms. This tool allows developers to transform and refactor code more easily.
  • Code Runner:- This tool features advanced code completion. You can deliver your code for most languages, including fuzzy-search, tab-selectable placeholders, and documentation snippets.
  • Fabric:- When it comes to iOS app development, Fabric is counted one of the best iOS app development tools. It allows developers to build better apps for a number of purposes.
  • AppCode:- AppCode, it is smart and reliable tool that is developed by JetBrains. This tool takes care of your routine tasks and saves you from extra coding.
  • TestFlight:- TestFlight is a very helpful tool, letting you invite users to test your iOS apps. You can collect valuable feedback before making your apps live on the App Store.
  • AppLyzer:- Applyzer is the best tool for those who want to gain insights of the app development market and app ranking.

5) What is Dictionary in Swift?

A dictionary is a type of hash table, providing fast access to the entries it contains. Each entry in the table is identified using its key, which is a hashable type such as a string or number. You use that key to retrieve the corresponding value, which can be any object.

6) What are optionals in Swift?

An optional in Swift is a type that can hold either a value or no value. Optionals are written by appending a ? to any type:

var name: String?

The above means that name can either be a string or does not contain anything which is represented by the ?. An optional is a kind of container.

7) What is use of ?? operator in Swift?

The nil-coalescing operator (a ?? b) unwraps an optional a if it contains a value, or returns a default value b if a is nil. The expression a is always of an optional type. The expression b must match the type that is stored inside a.

The nil-coalescing operator is shorthand for the code below:

a != nil ? a! : b

8) Explain Guard statement in Swift?

The main use of guard statement in Swift is to transfer program control out of scope on certain conditions. These statements are similar to if statements that execute statements based on a certain condition (boolean value) but unlike if, the guard statements only run when certain conditions are not met.

9) What is Enum in Swift?

"Enum" is short for "enumeration", and it’s a way of letting you use fixed names for special values rather than relying on strings or integers.

10) How to write multiple line comment in Swift?

Multiline comments in Swift start with a forward-slash followed by an asterisk (/*) and end with an asterisk followed by a forward-slash (*/). Everything in between /* and */ is ignored by the swift compiler.

Take Free: Swift MCQ & Quiz

11) Explain the Adapter and Memento Pattern?

Memento Pattern:- Memento pattern is a behavioral design pattern. Memento pattern is used to restore the state of an object to a previous state. As your application is progressing, you may want to save checkpoints in your application and restore back to those checkpoints later.

Adapter Pattern:- In software engineering, the adapter pattern is a software design pattern (also known as Wrapper, an alternative naming shared with the decorator pattern) that allows the interface of an existing class to be used as another interface.

12) What is Regular expression and Responder chain?

Regular Expression:- A regular expression, regex or regexp is a sequence of characters that define a search pattern. Usually, such patterns are used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation.

Responder chain:- The responder chain is a series of linked responder objects. It starts with the first responder and end with the app object. If the first responder cannot handle an event, it forwards the event to the next responder in the responder chain. A responder object is an object that can respond to and handle events.

13) What is difference between let an var in Swift?

The let keyword is used to declare constants while var is used for declaring variables.

let someConstant = 10
var someVariable : String

14) What are generics in Swift?

Swift language provides 'Generic' features to write flexible and reusable functions and types. Generics are used to avoid duplication and to provide abstraction. Swift 4 standard libraries are built with generics code. Swift 'Arrays' and 'Dictionary' types belong to generic collections.

15) What is difference between nil and .none in Swift?

There is no difference between nil and .none in Swift. None (. None for short) is the correct way of initializing an optional variable lacking a value, whereas nil is just syntactic sugar for.

16) What are benefits of using higher order functions?

Higher Order Functions in Swift (Sorted, Map, Filter, Reduce) are simply functions that operate on other functions by either taking a function as an argument or returning a function. These functions are useful for writing nice, clear, and concise code.

17) What is tuple? How to create a tuple in Swift?

Tuple in Swift is a group of different values represented as one. According to apple, a tuple type is a comma-separated list of zero or more types, enclosed in parentheses.

You can declare a tuple like any other variable or constant. To initialize it you will need another tuple or a tuple literal. A tuple literal is a list of values separated by commas between a pair of parentheses. You can use the dot notation to change the values from a tuple if it’s declared as a variable.


var point = (0, 0)
point.0 = 10
point.1 = 15
point // (10, 15)

18) What are delegates?

A delegate is a form of type-safe function pointer used by the Common Language Infrastructure (CLI). Delegates specify a method to call and optionally an object to call the method on. Delegates are used, among other things, to implement callbacks and event listeners.

19) Explain what is NSCache class?

The NSCache class incorporates various auto-removal policies, which ensure that it does not use too much of the system’s memory. The system automatically carries out these policies if memory is needed by other applications. When invoked, these policies remove some items from the cache, minimizing its memory footprint.

You can add, remove, and query items in the cache from different threads without having to lock the cache yourself.

20) What is Deinitializer in Swift?

Deinitialization is the process to deallocate or cleanup unused class instance objects to free a memory space occupied by the system resources for a better memory management.

A deinitializer is called immediately before a class instance is deallocated. You write deinitializers with the deinit keyword, similar to how initializers are written with the init keyword. Deinitializers are only available on class types.

21) What is the use of exclamation mark in Swift?

Swift uses exclamation marks(!) to signal both force unwrapping of optionals and explicitly unwrapped optionals.The exclamation mark indicates that the property of class is defined as an implicitly unwrapped optional.

22) Explain type aliasing in Swift?

Typealias in Swift is used to provide a new name for an existing data type in the program. Once you create a typealias, you can use the aliased name instead of the existing name throughout the program.

Typealias doesn't create a new data type, it simply provides a new name to the existing data type. The main objective of using typealias is to make our code clearer and human-readable.

23) How to get the length of a String in Swift?

In Swift 5.0 or above strings can be simply be treated as an array. You can use .count to get the length of the string in Swift.


24) What are Selectors in Swift?

Selectors are effectively the names of methods on an object or struct, and they are used to execute some code at runtime. They were common in Objective-C, but the earliest versions of Swift didn't include some core selector functionality so their use declined for a while.

25) What are different types of collections available in Swift?

Swift provides three primary collection types, known as arrays, sets, and dictionaries, for storing collections of values. Arrays are ordered collections of values. Sets are unordered collections of unique values. Dictionaries are unordered collections of key-value associations.

26) What are String Literals in Swift?

A string literal is a sequence of characters surrounded by double quotation marks (").

27) What is difference between single and double ? mark in Swift?

Single ? in Swift is used to denote an optional value either contains a value or contains nil to indicate that the value is missing.

double ?? in swift is called nil coalescing operator that finds if optional has no value then it uses a default value.

28) How to declare constant in Swift?

let keyword is used to declare a constant in Swift programming.

let street: String = "Swift Constant"

29) How to create an empty dictionary in Swift?

You can create an empty dictionary in Swift as below

 var emptyDictionary = [String: String]()

30) What are basic data types available in Swift?

Swift 4 offers the programmer a rich assortment of built-in as well as user-defined data types. The following types of basic data types are most frequently when declaring variables −  

  • Int or Uint − This is used for whole numbers. More specifically, you can use Int32, Int64 to define 32 or 64 bit signed integer, whereas UInt32 or UInt64 to define 32 or 64-bit unsigned integer variables. For example, 42 and -23.
  • Float − This is used to represent a 32-bit floating-point number and numbers with smaller decimal points. For example, 3.14159, 0.1, and -273.158.
  • Double − This is used to represent a 64-bit floating-point number and used when floating-point values must be very large. For example, 3.14159, 0.1, and -273.158.
  • Bool − This represents a Boolean value which is either true or false.
  • String − This is an ordered collection of characters. For example, "Hello, World!"
  • Character − This is a single-character string literal. For example, "C"
  • Optional − This represents a variable that can hold either a value or no value.
  • Tuples − This is used to group multiple values in single Compound Value.

31) What is forced unwrapping?

Forced unwrapping is an action done on the normal Optionals. Implicitly unwrapped Optionals are Optionals, usually used for class initialization and will pass values without exclamation mark when used.

Force unwrapping consists in adding a ! after an Optional value, to automatically unwrap it, without having to check whether it is nil or not.


let strings = ["mokacoding", "is", "a", "blog"]

let firstLength: Int = strings.first!.length

32) What is an in-out parameter in Swift?

An in-out parameter has a value that is passed into the function, is modified by the function, and is passed back out of the function to replace the original value. You write an in-out parameter by placing the inout keyword right before a parameter's type.

33) What is an attribute in Swift?

Swift Attributes provide information about a declaration or type.

There are two kinds of attributes in Swift:

  • Those are applied to declarations
  • Those that apply to types

34) What is half-open range operator in swift?

The half-open range operator (a..<b) defines a range that runs from a to b, but doesn’t include b. It’s said to be half-open because it contains its first value, but not its final value. As with the closed range operator, the value of a must not be greater than b. If the value of a is equal to b, then the resulting range will be empty.

35) What is init() in Swift?

Init() method in Swift is a predefined method for preparing an instance of a class, structure, or enumeration for use. This process involves setting an initial value for each stored property on that instance and performing any other setup or initialization that is required before the new instance is ready for use.

36) What is a Protocol in swift?

A Protocol in Swift defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements.

37) What is the difference between Array and NSArray?

The major difference between Array and NSArray is

Swift arrays are value Types which means that every object contained will be copied. NSArray are implemented as classes (and bridged from ObjC) so they're passed as references.

Swift Arrays are Generic <T> Structs meaning they are value types and are copied when assigned to another variable. In order to declare a swift array as immutable or mutable, you would use let or var.

Whereas, NSArray() Is a class and is Passed by reference, The only way to create another copy would be to use .copy(), but this still had some problems.

38) What is Grand Central Dispatch (GDC)?

Grand Central Dispatch (GDC), is a technology developed by Apple Inc. to optimize application support for systems with multi-core processors and other symmetric multiprocessing systems. It is an implementation of task parallelism based on the thread pool pattern.

39) What is made up of NSError object?

NSError object is made up of three critical pieces of information: a status code, corresponding to a particular error domain, as well as additional context provided by a userInfo dictionary.

40) What is @escaping Swift?

An escaping is a closure in swift that is called after the function it was passed to returns.

41) What is Flatmap in Swift?

Flatmap is used to flatten a collection of collections. It returns an array containing the concatenated results of calling the given transformation with each element of this sequence. Syntax

 func flatMap(_ transform: (Self.Element) throws -> SegmentOfResult) rethrows -> [SegmentOfResult.Element] where SegmentOfResult : Sequence

42) What is Variadic parameters in Swift?

A variadic parameter accepts zero or more values of a specified type. You use a variadic parameter to specify that the parameter can be passed a varying number of input values when the function is called.

43) What are initializer in Swift?

Initializers in Swift are called to create a new instance of a particular type. In its simplest form, an initializer is like an instance method with no parameters, written using the init keyword:

init() {
    // perform some initialization here

44) What is Self in Swift?

self in Swift is a property on the instance that refers to itself. It is used to access class, structure and enumeration instance within methods. It is the same as this keyword in Java and self in Objective-C.

45) What is Failable initializer Swift?

Failable initializers was introduced in Swift version 1.1. It is used to initialize the stored properties of a class or struct by providing initial values to each properties.

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