Extension syntax in Swift - Step-by-Step Execution

Concept Flow - Extension syntax

Start

↓

Define Extension

↓

Add new properties or methods

↓

Use extended type with new features

↓

End

The flow shows defining an extension, adding new features, then using them with the original type.

Execution Sample

Swift

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

let num = 4
print(num.squared())

This code adds a new method 'squared' to Int and uses it to print 16.

Execution Table

Step	Action	Evaluation	Result
1	Define extension on Int adding method squared()	Extension added	Int now has squared() method
2	Create constant num with value 4	num = 4	num stores 4
3	Call num.squared()	4 * 4	16
4	Print result of num.squared()	print(16)	Output: 16

💡 Execution ends after printing the squared value of num

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
num	undefined	4	4	4

Key Moments - 2 Insights

Can extensions add stored properties to a type?

No, extensions in Swift cannot add stored properties, only computed properties or methods. This is shown in Step 1 where only a method is added.

Does the original Int type change permanently after extension?

Yes, after defining the extension (Step 1), all Int values can use the new method, as seen in Step 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at Step 4?

A 4

B 16

C 8

D Error

💡 Hint

Check the 'Result' column in Step 4 of the execution_table.

At which step is the method 'squared()' added to Int?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column describing extension definition.

If we tried to add a stored property in the extension, what would happen?

A It would compile and work normally

B It would add the property only to new instances

C It would cause a compile-time error

D It would add the property only to existing instances

💡 Hint

Refer to the key moment about stored properties in extensions.

Concept Snapshot

Extension syntax in Swift:
- Use 'extension TypeName { }' to add new methods or computed properties.
- Cannot add stored properties.
- Extended features are available on all instances of the type.
- Useful to add functionality without subclassing or modifying original code.

Full Transcript

This visual trace shows how Swift extensions work. First, an extension is defined on Int to add a method called squared(). Then, a constant num is created with value 4. Calling num.squared() multiplies 4 by itself and returns 16. Finally, printing the result outputs 16. Extensions add new methods or computed properties but cannot add stored properties. Once defined, all Int values can use the new method.