Identity comparison (===) in Swift - Step-by-Step Execution

Concept Flow - Identity comparison (===)

Create Object A

↓

Create Object B

↓

Compare A === B?

Yes→Same Object

No↓

Different Objects

This flow shows creating two objects and then checking if they are exactly the same object in memory using ===.

Execution Sample

Swift

class Person {}
let p1 = Person()
let p2 = p1
let p3 = Person()
print(p1 === p2)
print(p1 === p3)

This code creates two Person objects and compares their identity using ===.

Execution Table

Step	Action	Evaluation	Result
1	Create p1 as new Person()	p1 points to Object1	p1 -> Object1
2	Assign p2 = p1	p2 points to same Object1 as p1	p2 -> Object1
3	Create p3 as new Person()	p3 points to Object2	p3 -> Object2
4	Evaluate p1 === p2	Are p1 and p2 same object?	true
5	Evaluate p1 === p3	Are p1 and p3 same object?	false

💡 All comparisons done, program ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
p1	nil	Object1	Object1	Object1	Object1
p2	nil	nil	Object1	Object1	Object1
p3	nil	nil	nil	Object2	Object2

Key Moments - 2 Insights

Why does p1 === p2 return true even though we didn't create a new object for p2?

Because p2 was assigned to p1, both variables point to the exact same object in memory, so identity comparison returns true (see execution_table step 4).

Why does p1 === p3 return false even though p3 is also a Person?

Because p3 is a new object created separately, so p1 and p3 point to different objects in memory, making identity comparison false (see execution_table step 5).

Visual Quiz - 3 Questions

Look at the execution table, what does p2 point to after step 2?

A nil

B A new Person object different from p1

C The same object as p1

D An error

💡 Hint

Check variable_tracker row for p2 after step 2.

At which step does p3 get assigned a new object?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at execution_table step 3 and variable_tracker for p3.

If we changed p2 = p1 to p2 = Person(), what would p1 === p2 return?

A true

B false

C nil

D Compile error

💡 Hint

New object means different identity, see explanation in key_moments.

Concept Snapshot

Identity comparison (===) checks if two variables point to the exact same object in memory.
Use === only with class instances (reference types).
If two variables refer to the same object, === returns true.
If they refer to different objects, even if identical in content, === returns false.
Useful to check object identity, not equality of content.

Full Transcript

This visual execution shows how identity comparison works in Swift using the === operator. We create two Person objects and assign variables p1, p2, and p3. p2 is assigned to p1, so both point to the same object. p3 is a new object. When we compare p1 === p2, it returns true because they are the same object. When we compare p1 === p3, it returns false because they are different objects. The variable tracker shows how variables point to objects step by step. Key moments clarify why assignment copies references, not objects, and why new objects have different identities. The quiz tests understanding of these points. The snapshot summarizes the concept simply.