Identity operators (=== and !==) in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if two class instances refer to the same object.

Swift

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

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

A==

B!==

C!=

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of === to check identity.

Confusing identity operators with equality operators.

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

2fill in blank

medium

Complete the code to check if two class instances do NOT refer to the same object.

Swift

if objectA [1] objectB {
    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 equality operators instead of identity operators.

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

3fill in blank

hard

Fix the error in the code to correctly check identity between two instances.

Swift

if person1 [1] person2 {
    print("They are the same person")
}

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

A===

B==

C!=

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which checks value equality, not identity.

Using !== which checks for non-identity.

Use === to check if two class instances are the same object in memory.

4fill in blank

hard

Fill both blanks to create a condition that prints "Same" if two objects are identical and "Different" if not.

Swift

if obj1 [1] obj2 {
    print("Same")
} else if obj1 [2] obj2 {
    print("Different")
}

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

A===

B==

C!==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality operators (==, !=) instead of identity operators.

Mixing up the order of operators.

The first blank uses === to check identity, the second uses !== to check non-identity.

5fill in blank

hard

Fill both blanks to create a function that returns true if two references are identical and false otherwise.

Swift

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

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

A===

B==

C?

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using equality operator instead of identity operator.

Forgetting to use the ternary operator correctly.

The function uses the identity operator === and the ternary operator ? : to return true if identical, else false.

Practice

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

easy

A. If two variables are of the same type

B. If two variables have the same value

C. If two variables refer to the exact same class instance

D. If two variables are both nil

Solution

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

   The === operator checks if two references point to the same object in memory.

2. Step 2: Differentiate from value equality

   Unlike ==, which checks value equality, === checks identity (same instance).

3. Final Answer:

   If two variables refer to the exact same class instance -> Option C

4. Quick Check:

   === checks identity [OK]

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

Common Mistakes:

• Confusing === with == for value equality
• Using === with structs or value types
• Thinking === checks type equality

2. Which of the following is the correct syntax to check if two class instances a and b are NOT the same object in Swift?

easy

A. if a != b

B. if a !==== b

C. if a !=== b

D. if a !== b

Solution

1. Step 1: Identify the correct identity operator for inequality

   The operator to check if two references are NOT the same object is !==.

2. Step 2: Verify syntax correctness

   Options C and D have invalid operators. if a != b uses != which checks value inequality, not identity.

3. Final Answer:

   if a !== b -> Option D

4. Quick Check:

   Use !== for identity inequality [OK]

Hint: Use !== to check different objects, not != [OK]

Common Mistakes:

• Using != instead of !== for identity check
• Typing invalid operators like !=== or !====
• Confusing identity operators with value operators

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. true\nfalse

B. false\ntrue

C. true\ntrue

D. false\nfalse

Solution

1. Step 1: Analyze the references

   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 A

4. Quick Check:

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

Hint: === true if same object, false if different [OK]

Common Mistakes:

• Assuming p1 and p3 are same because same class
• Confusing value equality with identity
• Forgetting p2 points to p1's instance

4. The following Swift code produces an error. What is the problem?

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

let p1 = Point(x: 1, y: 2)
let p2 = Point(x: 1, y: 2)

if p1 === p2 {
  print("Same point")
}

medium

A. p1 and p2 are not initialized

B. Cannot use === with structs because they are value types

C. Missing parentheses in if condition

D. === operator requires optional types

Solution

1. Step 1: Identify the types used

   Point is a struct, which is a value type in Swift.

2. Step 2: Understand identity operator restrictions

   Identity operators === and !== only work with class instances (reference types), not value types like structs.

3. Final Answer:

   Cannot use === with structs because they are value types -> Option B

4. Quick Check:

   === only for class instances [OK]

Hint: Use === only with classes, not structs or enums [OK]

Common Mistakes:

• Trying to use === with value types
• Assuming structs have identity
• Ignoring compiler error message

5. You have a class Car and an array of Car instances. You want to find if a specific Car instance myCar is already in the array by identity (same object), not by value. Which Swift code correctly checks this?

hard

A. if cars.contains(where: { $0 === myCar }) { print("Found") }

B. if cars.contains(myCar) { print("Found") }

C. if cars.firstIndex(of: myCar) != nil { print("Found") }

D. if cars.filter({ $0 == myCar }).count > 0 { 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 cars.contains(where: { $0 === myCar }) { print("Found") } uses === correctly. Options B and C use == or of: which check value equality or require Equatable conformance. if cars.filter({ $0 == myCar }).count > 0 { print("Found") } uses == which is value equality.

3. Final Answer:

   if cars.contains(where: { $0 === myCar }) { print("Found") } -> Option A

4. Quick Check:

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

Hint: Use contains(where:) with === to check object identity [OK]

Common Mistakes:

• Using contains(myCar) which checks value equality
• Assuming == checks identity
• Not using closure for identity check