Why protocol-oriented design matters in Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a protocol named 'Drivable'.

Swift

protocol [1] {
    func drive()
}

Drag options to blanks, or click blank then click option'

ACar

BDriveable

CDrivable

DVehicle

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a class name instead of a protocol name.

The protocol name should be 'Drivable' to match the design.

2fill in blank

medium

Complete the code to make 'Car' conform to the 'Drivable' protocol.

Swift

struct Car: [1] {
    func drive() {
        print("Car is driving")
    }
}

Drag options to blanks, or click blank then click option'

AVehicle

BRunnable

CDriveable

DDrivable

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong protocol name or a class name instead.

The struct 'Car' must conform to the 'Drivable' protocol to implement 'drive()'.

3fill in blank

hard

Fix the error in the code by completing the protocol method requirement.

Swift

protocol Drivable {
    func [1]()
}

struct Bike: Drivable {
    func drive() {
        print("Bike is driving")
    }
}

Drag options to blanks, or click blank then click option'

Adrive

Brun

Cstart

Dmove

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name than the one required by the protocol.

The protocol requires a method named 'drive()' which must be implemented by conforming types.

4fill in blank

hard

Fill both blanks to create a protocol extension that provides a default implementation.

Swift

protocol [1] {
    func start()
}

extension [2] {
    func start() {
        print("Starting...")
    }
}

Drag options to blanks, or click blank then click option'

AStartable

BRunnable

DDrivable

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for protocol and extension.

The protocol and its extension must have the same name 'Startable' to provide default behavior.

5fill in blank

hard

Fill all three blanks to create a protocol with a property and a method, then extend it with default behavior.

Swift

protocol [1] {
    var name: String { get }
    func [2]()
}

extension [3] {
    func greet() {
        print("Hello, \(name)!")
    }
}

Drag options to blanks, or click blank then click option'

AGreetable

Bgreet

DDrivable

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching protocol and extension names or method names.

The protocol 'Greetable' requires a 'name' property and a 'greet()' method. The extension provides a default 'greet()' implementation.

Practice

1. What is the main benefit of using protocols in Swift's protocol-oriented design?

easy

A. They make the code run faster.

B. They store data like variables.

C. They replace classes completely.

D. They allow different types to share common behavior.

Solution

1. Step 1: Understand what protocols do

   Protocols define a set of behaviors that many types can adopt and share.

2. Step 2: Identify the main benefit

   This sharing of behavior helps make code reusable and flexible.

3. Final Answer:

   They allow different types to share common behavior. -> Option D

4. Quick Check:

   Protocols = shared behavior [OK]

Hint: Protocols share behavior across types, not data storage [OK]

Common Mistakes:

• Thinking protocols speed up code execution
• Confusing protocols with classes
• Believing protocols store data

2. Which of the following is the correct way to declare a protocol in Swift?

easy

A. struct Vehicle: protocol { func drive() }

B. class Vehicle { func drive() }

C. protocol Vehicle { func drive() }

D. func protocol Vehicle() { drive() }

Solution

1. Step 1: Recall Swift protocol syntax

   Protocols are declared using the keyword 'protocol' followed by the name and curly braces.

2. Step 2: Match the correct syntax

   protocol Vehicle { func drive() } correctly uses 'protocol Vehicle { func drive() }'. Other options misuse keywords or structure.

3. Final Answer:

   protocol Vehicle { func drive() } -> Option C

4. Quick Check:

   Protocol declaration = protocol keyword + name + braces [OK]

Hint: Protocols start with 'protocol' keyword, not 'class' or 'func' [OK]

Common Mistakes:

• Using 'class' instead of 'protocol'
• Trying to inherit protocol with ':' in struct incorrectly
• Writing 'func protocol' which is invalid

3. Consider this Swift code:

protocol Greetable { func greet() -> String }

struct Person: Greetable {
  func greet() -> String { "Hello!" }
}

let p = Person()
print(p.greet())

What will be the output?

medium

A. Hello!

B. greet()

C. Error: Missing function implementation

D. nil

Solution

1. Step 1: Check protocol conformance

   Person struct implements the greet() method required by Greetable.

2. Step 2: Understand the print output

   Calling p.greet() returns "Hello!", which is printed.

3. Final Answer:

   Hello! -> Option A

4. Quick Check:

   Implemented method returns "Hello!" [OK]

Hint: Implemented protocol methods run normally when called [OK]

Common Mistakes:

• Assuming protocol methods print their name
• Expecting runtime error without implementation
• Thinking print outputs nil if no return

4. What is wrong with this Swift code?

protocol Drawable {
  func draw()
}

struct Circle: Drawable {
  // Missing draw() implementation
}

let c = Circle()

medium

A. Circle must implement draw() or code won't compile.

B. Circle can omit draw() because it's a struct.

C. Protocol Drawable should not have functions.

D. Circle should be a class, not a struct.

Solution

1. Step 1: Check protocol requirements

   Drawable requires any conforming type to implement draw().

2. Step 2: Verify Circle implementation

   Circle does not implement draw(), so it violates the protocol.

3. Final Answer:

   Circle must implement draw() or code won't compile. -> Option A

4. Quick Check:

   Protocol methods must be implemented [OK]

Hint: All protocol methods must be implemented to compile [OK]

Common Mistakes:

• Thinking structs can skip protocol methods
• Believing protocols can't have functions
• Confusing struct vs class requirements

5. You want to design a system where multiple types like Car and Bicycle can be "startable" with a start() method. Using protocol-oriented design, which approach is best?

hard

A. Write separate start() functions outside the types for each vehicle.

B. Create a protocol Startable with start() and have both types conform to it.

C. Make Car and Bicycle subclasses of a common class with start() method.

D. Use global variables to track if Car or Bicycle started.

Solution

1. Step 1: Identify shared behavior

   Both Car and Bicycle need a start() method, which is shared behavior.

2. Step 2: Apply protocol-oriented design

   Defining a Startable protocol with start() and making both types conform promotes reuse and flexibility.

3. Step 3: Compare other options

   Subclassing limits flexibility; separate functions or globals reduce clarity and reuse.

4. Final Answer:

   Create a protocol Startable with start() and have both types conform to it. -> Option B

5. Quick Check:

   Protocol for shared behavior = best design [OK]

Hint: Use protocols to share behavior across unrelated types [OK]

Common Mistakes:

• Using class inheritance when unrelated types
• Writing separate functions instead of protocol
• Using global state instead of behavior abstraction