Swift scope: variables inside blocks

Goal

Understand how scope controls where variables and constants can be used.

• Focus on values declared inside if, else, and func blocks.
• Learn how to avoid “cannot find in scope” errors.

if true {
    let message = "Inside"
    print(message)
}

// print(message)  // Error: message is out of scope

What is scope?

Scope is the region of code where a name is visible.

• Variables and constants exist only inside the block they are declared in.
• When the block ends, those names are no longer accessible.

func showTitle() {
    let title = "Room calculator"
    print(title)
}

// print(title)  // Error: title is out of scope

Why developers care about scope

Scope prevents accidental changes to values that should be private.

• It keeps code organized so each block controls its own data.
• It reduces bugs by limiting where variables can be used.

func calculate() {
    let roomLength = 6.0
    let roomWidth = 4.5
    let area = roomLength * roomWidth
    print(area)
}

Scope in an if block

A value declared inside an if block exists only inside that block.

• You can use it inside the braces but not after the block ends.

let hasFurniture = true

if hasFurniture {
    let furnitureCount = 3
    print(furnitureCount)
}

// print(furnitureCount)  // Error

Scope in else blocks

Each branch has its own scope.

• Values declared in if are not visible in else and vice versa.

let isLarge = false

if isLarge {
    let label = "Large room"
    print(label)
} else {
    let label = "Small room"
    print(label)
}

// print(label)  // Error

Scope in functions

All variables declared inside a function are local to that function.

• They cannot be used by code outside the function.
• This makes functions independent and reusable.

func roomVolume() {
    let length = 6.0
    let width = 4.5
    let height = 2.7
    let volume = length * width * height
    print(volume)
}

// print(volume)  // Error

Using values outside a block

Declare the variable before the block if you need it later.

• Then assign it inside the block.
• Make sure it always gets a value before you use it.

var message = ""

if true {
    message = "Inside"
}

print(message)

Common scope errors

Using a variable outside its block causes a “cannot find in scope” error.

• Declaring a new variable with the same name can hide the outer one.
• Forgetting to initialize a variable before use causes another error.

var result = 0

if true {
    let result = 10
    print(result)
}

print(result)  // This prints the outer value

How to test scope behavior

Move a variable inside or outside a block and observe the compiler error.

• Check which variables appear in code completion at each line.
• Use print statements to confirm which value is in scope.

if true {
    let x = 5
    print(x)
}

// print(x)  // Uncomment to see the error

Task A

if true {
    let note = "Inside"
    // print inside the block
}

// try to print note here

Task B

var status = ""

if true {
    // assign a value here
}

// print status here

Task C

func showArea() {
    // declare three constants
    // calculate area and print it
}

// try to print the area here

Task D

let isLarge = false

if isLarge {
    // declare a label and print it
} else {
    // declare a label and print it
}

// try to print label here