Identity comparison (===) in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if two class instances are the same object using identity comparison.

Swift

if object1 [1] object2 {
    print("Same instance")
} else {
    print("Different instances")
}

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

A===

B==

C=

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of === for identity comparison

Using = which is assignment, not comparison

In Swift, the identity comparison operator is ===. It checks if two references point to the exact same object.

2fill in blank

medium

Complete the code to print "Same" if two variables refer to the same instance using identity comparison.

Swift

if person1 [1] person2 {
    print("Same")
} else {
    print("Not same")
}

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

A==

B!==

C!=

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing equality (==) with identity (===)

Using !== which checks for not identical

The === operator checks if two variables refer to the same instance in memory.

3fill in blank

hard

Fix the error in the code to correctly check if two class instances are not the same using identity comparison.

Swift

if objectA [1] objectB {
    print("Different instances")
} else {
    print("Same instance")
}

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

A!=

B!==

C===

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using != which checks for inequality but not identity

Using === which checks for identity, not difference

The operator !== checks if two references do not point to the same object.

4fill in blank

hard

Fill both blanks to create a function that returns true if two class instances are identical.

Swift

func areIdentical(_ a: AnyObject, _ b: AnyObject) -> Bool {
    return a [1] b [2] true
}

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

A!=

B==

C===

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of === for identity

Using != or !== incorrectly

The function uses === to check identity and returns true if they are the same instance.

5fill in blank

hard

Fill all three blanks to create a function that returns true if two instances are not identical.

Swift

func areNotIdentical(_ x: AnyObject, _ y: AnyObject) -> Bool {
    if x [1] y {
        return [2]
    } else {
        return [3]
    }
}

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

A!==

Btrue

Cfalse

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Using === instead of !== for not identical

Returning wrong boolean values

The function uses !== to check if two references are not identical, returning true if so, otherwise false.

Practice

1. What does the === operator check in Swift?

easy

A. If two variables refer to the exact same object instance

B. If two variables have the same value

C. If two variables are of the same type

D. If two variables are both nil

Solution

1. Step 1: Understand the purpose of ===

   The === operator in Swift is used to check if two references point to the exact same object in memory.

2. Step 2: Differentiate from value equality

   Unlike ==, which checks if values are equal, === checks identity, meaning the same instance.

3. Final Answer:

   If two variables refer to the exact same object instance -> Option A

4. Quick Check:

   Identity comparison = If two variables refer to the exact same object instance [OK]

Hint: Remember: === means same object, not just equal value [OK]

Common Mistakes:

• Confusing === with == for value equality
• Thinking === checks type equality
• Assuming === works with structs or enums

2. Which of the following is the correct syntax to check if two class instances a and b are identical in Swift?

easy

A. if a === b { }

B. if a == b { }

C. if a = b { }

D. if a is b { }

Solution

1. Step 1: Recall identity operator syntax

   In Swift, the identity operator to check if two references point to the same object is ===.

2. Step 2: Identify correct usage

   The correct syntax is if a === b { }. The other options are either value equality, assignment, or invalid syntax.

3. Final Answer:

   if a === b { } -> Option A

4. Quick Check:

   Identity check syntax = if a === b { } [OK]

Hint: Use three equals signs (===) for identity check [OK]

Common Mistakes:

• Using == instead of === for identity
• Using single = which is assignment
• Typing invalid operators like ===

3. Consider the following Swift code:

class Person {}

let p1 = Person()
let p2 = p1
let p3 = Person()

print(p1 === p2)
print(p1 === p3)

What will be the output?

medium

A. false\nfalse

B. false\ntrue

C. true\ntrue

D. true\nfalse

Solution

1. Step 1: Analyze object references

   Variable p2 is assigned to p1, so both point to the same object. p3 is a new instance.

2. Step 2: Evaluate identity comparisons

   p1 === p2 is true because they are the same instance. p1 === p3 is false because they are different instances.

3. Final Answer:

   true\nfalse -> Option D

4. Quick Check:

   Same instance = true, different instance = false [OK]

Hint: Same variable means true; new instance means false [OK]

Common Mistakes:

• Assuming different variables always mean false
• Confusing === with == and expecting value equality
• Ignoring that p2 points to p1's instance

4. The following Swift code gives a compile error. What is the problem?

class Car {}

let car1 = Car()
let car2 = Car()

if car1 == car2 {
    print("Same car")
}

medium

A. Cannot create instances of class Car

B. Missing parentheses in if statement

C. Cannot use == to compare class instances without Equatable conformance

D. Using === instead of ==

Solution

1. Step 1: Understand == operator requirements

   By default, class instances cannot be compared with == unless the class conforms to Equatable.

2. Step 2: Identify the error cause

   The code tries to use == without Car conforming to Equatable, causing a compile error.

3. Final Answer:

   Cannot use == to compare class instances without Equatable conformance -> Option C

4. Quick Check:

   == needs Equatable for classes [OK]

Hint: Use === for identity or add Equatable for == [OK]

Common Mistakes:

• Thinking === causes error here
• Assuming == works automatically for classes
• Ignoring Equatable protocol requirement

5. You have a cache dictionary storing class instances by keys. You want to check if a newly created instance newObj is already stored in the cache by identity. Which Swift code correctly checks this?

class Data {}

var cache: [String: Data] = [:]
let newObj = Data()

// Check if newObj is already in cache by identity

hard

A. if cache.values.contains(newObj) { print("Found") }

B. if cache.values.contains(where: { $0 === newObj }) { print("Found") }

C. if cache.keys.contains(where: { $0 === newObj }) { print("Found") }

D. if cache.values.contains(where: { $0 == newObj }) { print("Found") }

Solution

1. Step 1: Understand identity check in collections

   To check if an instance exists by identity, use === inside a closure with contains(where:).

2. Step 2: Analyze options

   if cache.values.contains(where: { $0 === newObj }) { print("Found") } correctly uses cache.values.contains(where: { $0 === newObj }). if cache.values.contains(newObj) { print("Found") } uses contains without identity check, which requires Equatable. if cache.keys.contains(where: { $0 === newObj }) { print("Found") } incorrectly checks keys (strings) with identity. if cache.values.contains(where: { $0 == newObj }) { print("Found") } uses == which needs Equatable.

3. Final Answer:

   if cache.values.contains(where: { $0 === newObj }) { print("Found") } -> Option B

4. Quick Check:

   Use contains(where:) with === for identity [OK]

Hint: Use contains(where:) and === to check identity in collections [OK]

Common Mistakes:

• Using contains without where and identity check
• Checking keys instead of values
• Using == without Equatable conformance