Identity operators (=== and !==) in Swift - Mini Project: Build & Apply

Identity Operators (=== and !==) in Swift

📖 Scenario: Imagine you are managing a list of pets in a pet shelter. Each pet is represented by an object. Sometimes, you want to check if two variables point to the exact same pet object, not just pets that look alike.

🎯 Goal: You will create two pet objects, then use Swift's identity operators === and !== to check if two variables refer to the same object.

📋 What You'll Learn

Create two instances of a class called Pet with a name property

Create two variables referencing these instances

Use the identity operator === to check if two variables refer to the same object

Use the identity operator !== to check if two variables do not refer to the same object

Print the results of these identity checks

💡 Why This Matters

🌍 Real World

In real apps, identity operators help check if two variables point to the same object in memory, which is important when managing shared resources or references.

💼 Career

Understanding identity operators is useful for Swift developers working on iOS apps, especially when handling object references, memory management, and debugging.

1

Create two Pet objects

Create a class called Pet with a property name of type String. Then create two instances called pet1 with name "Buddy" and pet2 with name "Buddy".

Swift

class Pet {
    var name: String
    init(name: String) {
        self.name = name
    }
}

// Create pet1 and pet2 instances below
# Your code here

Hint

Define the class with a name property and an initializer. Then create two separate instances with the same name.

2

Create a third variable referencing pet1

Create a variable called pet3 and assign it to reference the same object as pet1.

Swift

class Pet {
    var name: String
    init(name: String) {
        self.name = name
    }
}

let pet1 = Pet(name: "Buddy")
let pet2 = Pet(name: "Buddy")

// Create pet3 referencing pet1 below
# Your code here

Hint

Assign pet3 to pet1 so both point to the same object.

3

Use identity operators to compare pets

Use if statements with the identity operator === to check if pet1 and pet3 refer to the same object, and if pet1 and pet2 refer to the same object. Store the results in variables samePet1and3 and samePet1and2 respectively.

Swift

class Pet {
    var name: String
    init(name: String) {
        self.name = name
    }
}

let pet1 = Pet(name: "Buddy")
let pet2 = Pet(name: "Buddy")
let pet3 = pet1

// Use identity operators to compare pet1 and pet3, pet1 and pet2
# Your code here

Hint

Use === to check if two variables point to the same object and assign the result to variables.

4

Print the results of identity checks

Print the values of samePet1and3 and samePet1and2 using print statements.

Swift

class Pet {
    var name: String
    init(name: String) {
        self.name = name
    }
}

let pet1 = Pet(name: "Buddy")
let pet2 = Pet(name: "Buddy")
let pet3 = pet1

let samePet1and3 = (pet1 === pet3)
let samePet1and2 = (pet1 === pet2)

// Print the results below
# Your code here

Hint

Use print to show the boolean results of the identity checks.

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