Iterating enum cases with CaseIterable in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the enum conform to CaseIterable.

Swift

enum Direction: [1] {
    case north, south, east, west
}

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

ACaseIterable

BCodable

CEquatable

DHashable

Attempts:

3 left

💡 Hint

Common Mistakes

Using other protocols like Codable or Equatable which do not provide case iteration.

To iterate over all enum cases, the enum must conform to CaseIterable.

2fill in blank

medium

Complete the code to print all cases of the enum.

Swift

for direction in Direction.[1] {
    print(direction)
}

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Acases

Bvalues

CallCases

Delements

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect property names like 'cases' or 'values' which do not exist.

The CaseIterable protocol provides the allCases property to access all enum cases.

3fill in blank

hard

Fix the error in the code to correctly iterate over enum cases.

Swift

enum Color: CaseIterable {
    case red, green, blue
}

for color in Color.[1]() {
    print(color)
}

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AallCases

BallCases()

Ccases

Dall_cases

Attempts:

3 left

💡 Hint

Common Mistakes

Calling allCases with parentheses like a function.

allCases is a property, not a method, so it should not have parentheses.

4fill in blank

hard

Fill both blanks to create a dictionary with enum case names as keys and raw values as values.

Swift

enum Fruit: String, CaseIterable {
    case apple = "Red"
    case banana = "Yellow"
    case grape = "Purple"
}

let fruitColors = [[1]: [2] for fruit in Fruit.allCases]

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Afruit.rawValue

Bfruit

Cfruit.name

Dfruit.description

Attempts:

3 left

💡 Hint

Common Mistakes

Using fruit.name or fruit.description which do not exist.

Use the enum case itself as the key and its rawValue as the value.

5fill in blank

hard

Fill all three blanks to filter enum cases with raw value length greater than 5 and create a list of their names.

Swift

enum Vehicle: String, CaseIterable {
    case car = "Auto"
    case motorcycle = "Motorcycle"
    case bicycle = "Bike"
    case airplane = "Airplane"
}

let longNames = [[1] for vehicle in Vehicle.allCases if [2].[3] > 5]

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Avehicle.rawValue

Bcount

Cvehicle

Attempts:

3 left

💡 Hint

Common Mistakes

Using the enum case itself instead of raw values.

Checking length on the enum case instead of the raw value.

We want the raw value names where the length is greater than 5. So we use vehicle.rawValue in the list and check vehicle.rawValue.count > 5.

Practice

1. What does the CaseIterable protocol allow you to do with an enum in Swift?

easy

A. Make enum cases private

B. Access all enum cases as a collection

C. Add stored properties to enum cases

D. Change enum cases at runtime

Solution

1. Step 1: Understand the purpose of CaseIterable

   The CaseIterable protocol provides a way to access all cases of an enum as a collection.

2. Step 2: Identify what CaseIterable does not do

   It does not allow changing cases, adding stored properties, or changing access levels.

3. Final Answer:

   Access all enum cases as a collection -> Option B

4. Quick Check:

   CaseIterable = Access all cases [OK]

Hint: Remember: CaseIterable gives you all enum cases easily [OK]

Common Mistakes:

• Thinking CaseIterable allows modifying enum cases
• Confusing CaseIterable with adding properties
• Assuming CaseIterable changes access control

2. Which of the following is the correct way to declare an enum that supports iteration over all its cases using CaseIterable?

easy

A. enum Direction: CaseIterable { case north, south, east, west }

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

C. enum Direction: Iterable { case north, south, east, west }

D. enum Direction: CaseIterable() { case north, south, east, west }

Solution

1. Step 1: Check correct protocol conformance syntax

   In Swift, you conform to a protocol by listing it after a colon without parentheses.

2. Step 2: Identify the correct protocol name

   The correct protocol is CaseIterable, not Iterable, and no parentheses are used.

3. Final Answer:

   enum Direction: CaseIterable { case north, south, east, west } -> Option A

4. Quick Check:

   Correct syntax = enum Direction: CaseIterable { case north, south, east, west } [OK]

Hint: Use ': CaseIterable' without parentheses to conform [OK]

Common Mistakes:

• Adding parentheses after CaseIterable
• Using wrong protocol name like Iterable
• Forgetting to conform to CaseIterable

3. Given the enum below, what will be printed by the code?

enum Fruit: CaseIterable {
    case apple, banana, cherry
}

for fruit in Fruit.allCases {
    print(fruit)
}

medium

A. apple banana cherry

B. ["apple", "banana", "cherry"]

C. apple
banana
cherry

D. Fruit.apple Fruit.banana Fruit.cherry

Solution

1. Step 1: Understand the for loop over allCases

   The loop iterates over each case in the enum and prints it on a new line.

2. Step 2: Recognize print behavior in Swift

   Each call to print outputs the case name followed by a newline.

3. Final Answer:

   apple banana cherry -> Option C

4. Quick Check:

   Loop prints each case on separate lines [OK]

Hint: print() adds new line after each output [OK]

Common Mistakes:

• Assuming all cases print on one line
• Expecting array output instead of separate lines
• Confusing enum case names with full type names

4. What is wrong with this code snippet?

enum Color: CaseIterable {
    case red, green, blue
}

for color in Color {
    print(color)
}

medium

A. The enum cases must be strings

B. The enum must be a class to iterate

C. CaseIterable requires a raw value type

D. You must use Color.allCases to iterate, not Color directly

Solution

1. Step 1: Identify how to iterate over enum cases

   You cannot iterate over the enum type itself; you must use allCases property.

2. Step 2: Understand CaseIterable usage

   CaseIterable provides allCases which returns a collection of all enum cases for iteration.

3. Final Answer:

   You must use Color.allCases to iterate, not Color directly -> Option D

4. Quick Check:

   Use allCases for iteration [OK]

Hint: Always loop over Enum.allCases, not Enum itself [OK]

Common Mistakes:

• Trying to loop over enum type directly
• Thinking CaseIterable needs raw values
• Assuming enum must be a class

5. You want to create a menu that lists all payment methods defined in this enum:

enum PaymentMethod: CaseIterable {
    case cash, creditCard, paypal, applePay
}

Which code snippet correctly prints each payment method with a number starting from 1?

hard

A. for (index, method) in PaymentMethod.allCases.enumerated() {
print("\(index + 1). \(method)")
}

B. for method in PaymentMethod.allCases {
print("\(method + 1). \(method)")
}

C. for index in 1...PaymentMethod.allCases.count {
print("\(index). \(PaymentMethod.allCases[index])")
}

D. for method in PaymentMethod {
print("\(method.rawValue + 1). \(method)")
}

Solution

1. Step 1: Use enumerated() to get index and value

   The enumerated() method returns pairs of (index, element) for the collection.

2. Step 2: Adjust index to start from 1 and print

   Since enumerated indexes start at 0, add 1 to show numbering from 1.

3. Final Answer:

   for (index, method) in PaymentMethod.allCases.enumerated() { print("\(index + 1). \(method)") } -> Option A

4. Quick Check:

   Use enumerated() + index+1 for numbering [OK]

Hint: Use enumerated() and add 1 to index for numbering [OK]

Common Mistakes:

• Trying to add 1 directly to enum case
• Indexing allCases with 1-based index (off by one)
• Looping over enum type instead of allCases