Extending built-in types in Swift - Step-by-Step Execution

Concept Flow - Extending built-in types

Start

↓

Define Extension

↓

Add new method/property

↓

Use extended type

↓

Call new method/property

↓

Get result

↓

End

You start by defining an extension to a built-in type, add new methods or properties, then use the extended type to call those new features.

Execution Sample

Swift

extension Int {
    func squared() -> Int {
        return self * self
    }
}

let number = 5
print(number.squared())

This code adds a new method 'squared' to Int that returns the number multiplied by itself, then prints 25.

Execution Table

Step	Action	Evaluation	Result
1	Define extension Int with method squared()	Extension created	Int now has squared() method
2	Create constant number = 5	number assigned 5	number = 5
3	Call number.squared()	Calculate 5 * 5	25
4	Print result	Output 25	Console shows 25

💡 Program ends after printing the squared value

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
number	undefined	5	5	5
result of squared()	undefined	undefined	25	25

Key Moments - 2 Insights

Why can we call squared() on an Int even though Int doesn't have it originally?

Because the extension adds the squared() method to Int before we call it, as shown in step 1 of the execution_table.

Does the original Int type change permanently after extension?

No, extensions add functionality only in the current scope or module; the original Int type remains unchanged elsewhere.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'number' after step 2?

A undefined

B 25

C 5

D 0

💡 Hint

Check the 'variable_tracker' table under 'number' after Step 2

At which step is the squared() method actually called?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in the execution_table for when number.squared() is called

If we changed number to 3, what would be the output at step 4?

A 6

B 9

C 3

D 25

💡 Hint

Recall squared() returns number * number; see execution_table step 3 for calculation

Concept Snapshot

Swift extensions let you add new methods or properties to existing types.
Syntax: extension TypeName { func newMethod() { } }
You can call new methods on instances as if built-in.
Extensions do not modify original type permanently.
Useful to add functionality without subclassing.

Full Transcript

This example shows how to extend Swift's built-in Int type by adding a new method called squared(). The extension is defined first, adding the method that returns the number multiplied by itself. Then, a constant number is created with value 5. Calling number.squared() runs the new method, calculating 25. Finally, the result 25 is printed to the console. The execution table traces each step: defining the extension, creating the number, calling squared(), and printing the result. The variable tracker shows how 'number' stays 5 and the squared() result is 25. Key moments clarify that extensions add methods to types so you can call them like built-in methods, but the original type is not permanently changed. The quiz tests understanding of variable values and method calls during execution. The snapshot summarizes how extensions work in Swift simply and clearly.