Why Identity operators (=== and !==) in Swift? - Purpose & Use Cases

The Big Idea

What if you could instantly know if two things are truly one and the same, not just lookalikes?

The Scenario

Imagine you have two boxes that look the same and hold the same toys, but you want to know if they are actually the exact same box, not just similar.

The Problem

Without identity operators, you might compare the contents of the boxes and get confused if they look alike but are actually different boxes. This can lead to mistakes and extra work checking each box carefully.

The Solution

Identity operators (=== and !==) let you quickly check if two things are the exact same object in memory, like checking if two keys open the same lock, saving time and avoiding errors.

Before vs After

✗ Before

if box1 == box2 { print("Boxes look the same") }

✓ After

if box1 === box2 { print("Boxes are the exact same") }

What It Enables

This lets you easily tell if two variables point to the same object, which is crucial for managing shared resources or avoiding duplicate work.

Real Life Example

When building an app, you might want to know if two buttons are actually the same button instance to update it correctly without creating duplicates.

Key Takeaways

Identity operators check if two references point to the exact same object.

They help avoid confusion between similar but different objects.

Using them makes your code clearer and more efficient when managing objects.

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