Equatable, Hashable, Comparable protocols in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the struct conform to Equatable.

Swift

struct Point: Equatable {
    var x: Int
    var y: Int

    static func ==(lhs: Point, rhs: Point) -> Bool {
        return lhs.x [1] rhs.x && lhs.y == rhs.y
    }
}

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

A+

B==

C!=

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes the comparison to be wrong.

Using '+' or '-' operators here does not make sense.

The == operator checks if both x and y are equal for two points.

2fill in blank

medium

Complete the code to make the struct conform to Hashable by implementing hash(into:).

Swift

struct Person: Hashable {
    var name: String
    var age: Int

    func hash(into hasher: inout Hasher) {
        hasher.[1](name)
        hasher.combine(age)
    }
}

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

Aappend

Badd

Cinsert

Dcombine

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' or 'add' which are not methods of Hasher.

Forgetting to combine all properties.

The combine method adds the value to the hasher to create a hash.

3fill in blank

hard

Fix the error in the Comparable conformance by completing the less-than operator.

Swift

struct Rectangle: Comparable {
    var width: Int
    var height: Int

    static func < (lhs: Rectangle, rhs: Rectangle) -> Bool {
        return lhs.width [1] rhs.width
    }
}

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

A<

B>

C==

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or >= reverses the comparison logic.

Using == does not define ordering.

The less-than operator < compares if the left width is smaller than the right width.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps words to their lengths only if length is greater than 3.

Swift

let words = ["apple", "cat", "banana", "dog"]
var lengths = [String: Int]()
for word in words {
    if word.[1] > 3 {
        lengths[word] = word.[2]
    }
}

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

Acount

Blength

Csize

DlengthOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using properties like 'length' or 'size' which do not exist in Swift strings.

Using different properties for the two blanks causes errors.

The count property gives the number of characters in a string.

5fill in blank

hard

Fill all three blanks to create a sorted array of unique names using Set and sorted().

Swift

let names = ["Anna", "Bob", "Anna", "Charlie"]
let uniqueSortedNames = Array([1](names)).[2]() [3] { $0 < $1 }

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

ASet

Bsorted

Csorted(by:)

DArray

Attempts:

3 left

💡 Hint

Common Mistakes

Using sorted() without by: when a closure is provided causes errors.

Not converting back to Array if needed.

First, convert the array to a Set to remove duplicates. Then use sorted(by:) with a closure to sort ascending. Finally, Array converts the set back to an array.

Practice

1.

Which protocol in Swift allows you to check if two instances of a type are equal using ==?

easy

A. Hashable

B. Codable

C. Comparable

D. Equatable

Solution

1. Step 1: Understand the purpose of Equatable

   Equatable protocol allows comparing two instances for equality using ==.

2. Step 2: Compare with other protocols

   Hashable is for hashing, Comparable is for ordering, Codable is for encoding/decoding.

3. Final Answer:

   Equatable -> Option D

4. Quick Check:

   Equality check = Equatable [OK]

Hint: Equality means Equatable protocol [OK]

Common Mistakes:

• Confusing Hashable with Equatable
• Thinking Comparable checks equality
• Mixing Codable with Equatable

2.

Which of the following is the correct way to declare a struct Person that conforms to Equatable and Hashable?

struct Person: ??? {
    var name: String
    var age: Int
}

easy

A. Equatable, Hashable

B. Comparable, Hashable

C. Equatable, Comparable

D. Codable, Hashable

Solution

1. Step 1: Identify needed protocols

   To compare equality and use in sets/dictionaries, use Equatable and Hashable.

2. Step 2: Check syntax for protocol conformance

   Protocols are listed separated by commas after colon in struct declaration.

3. Final Answer:

   Equatable, Hashable -> Option A

4. Quick Check:

   Equality + hashing = Equatable, Hashable [OK]

Hint: List protocols comma-separated after colon [OK]

Common Mistakes:

• Using Comparable instead of Equatable
• Forgetting commas between protocols
• Using Codable instead of Equatable

3.

What will be the output of the following Swift code?

struct Item: Comparable {
    var value: Int
    static func < (lhs: Item, rhs: Item) -> Bool {
        return lhs.value < rhs.value
    }
}

let items = [Item(value: 3), Item(value: 1), Item(value: 2)]
let sortedValues = items.sorted().map { $0.value }
print(sortedValues)

medium

A. [3, 2, 1]

B. [1, 2, 3]

C. [2, 3, 1]

D. Compilation error

Solution

1. Step 1: Understand Comparable conformance

   The < operator compares value properties to sort ascending.

2. Step 2: Analyze sorting and mapping

   Sorting the array orders items by value: 1, 2, 3. Mapping extracts values in this order.

3. Final Answer:

   [1, 2, 3] -> Option B

4. Quick Check:

   Sorted values ascending = [1, 2, 3] [OK]

Hint: Comparable sorts ascending by < operator [OK]

Common Mistakes:

• Assuming descending order by default
• Confusing map output with original array
• Forgetting to implement < operator

4.

Identify the error in this Swift struct that tries to conform to Hashable:

struct Book: Hashable {
    var title: String
    var pages: Int

    func hash(into hasher: inout Hasher) {
        hasher.combine(title)
    }
}

medium

A. Missing combine call for all properties in hash(into:)

B. Struct cannot conform to Hashable without Codable

C. Incorrect method signature for hash(into:)

D. Missing == operator implementation for Equatable

Solution

1. Step 1: Check Hashable requirements

   Hashable requires hashing all properties that affect equality.

2. Step 2: Analyze hash(into:) implementation

   Only title is combined; pages is missing, causing incorrect hashing.

3. Final Answer:

   Missing combine call for all properties in hash(into:) -> Option A

4. Quick Check:

   Hash all relevant properties [OK]

Hint: Hash all properties used in equality [OK]

Common Mistakes:

• Hashing only some properties
• Forgetting to implement == operator if needed
• Wrong method signature for hash(into:)

5.

You want to create a struct Player that can be stored in a Set, compared for equality, and sorted by score descending. Which protocols should Player conform to, and how should you implement the sorting?

hard

A. Conform to Equatable and Hashable; implement < to compare scores descending

B. Conform to Comparable only; implement < to compare scores ascending

C. Conform to Equatable, Hashable, Comparable; implement < to compare scores descending

D. Conform to Hashable only; sorting is automatic

Solution

1. Step 1: Identify needed protocols

   To store in Set and check equality, conform to Equatable and Hashable. To sort, conform to Comparable.

2. Step 2: Implement sorting logic

   Implement < operator to compare scores descending by reversing comparison.

3. Final Answer:

   Conform to Equatable, Hashable, Comparable; implement < for descending scores -> Option C

4. Quick Check:

   Set + equality + custom sort = Equatable, Hashable, Comparable [OK]

Hint: Use all three protocols; reverse < for descending sort [OK]

Common Mistakes:

• Forgetting Comparable for sorting
• Sorting ascending instead of descending
• Missing Equatable or Hashable for Set storage