30 Days of SwiftUI — Day 2: Understanding Collections and Enums in Swift

 

Introduction

As we continue our SwiftUI learning journey, understanding how to store and organize data efficiently is crucial. Today, we’ll explore arrays, dictionaries, sets, enums, and type annotations — fundamental concepts that make data handling easier and more structured in Swift.

Storing Ordered Data in Arrays

An array is a collection that stores data in an ordered manner. Arrays allow duplicates and maintain the order of elements.

Creating an Array

var fruits = ["Apple", "Banana", "Mango"]

Alternatively, you can define an array with explicit type annotation:

var numbers: [Int] = [10, 20, 30, 40]

Accessing Elements

You can access elements using index positions (starting from 0):

print(fruits[1]) // Output: Banana

Modifying an Array

fruits.append("Orange") // Adds "Orange" at the end
fruits.remove(at: 0) // Removes "Apple"
print(fruits) // Output: ["Banana", "Mango", "Orange"]

Storing and Finding Data in Dictionaries

A dictionary is a collection that stores data in key-value pairs, allowing for fast lookups.

Creating a Dictionary

var studentScores = ["Alice": 90, "Bob": 85, "Charlie": 88]

Accessing Values

print(studentScores["Alice"]) // Output: Optional(90)

Since a key may not exist, Swift returns an Optional. You can safely unwrap it using if let:

if let score = studentScores["Bob"] {
    print("Bob's score is \(score)")
}

Modifying a Dictionary

studentScores["David"] = 92 // Adding a new key-value pair
studentScores["Alice"] = 95 // Updating an existing value
print(studentScores)

Using Sets for Fast Data Lookup

A set is an unordered collection that ensures unique values and provides fast lookup times.

Creating a Set

var uniqueNumbers: Set<Int> = [1, 2, 3, 4, 5]

Adding and Removing Elements

uniqueNumbers.insert(6)
uniqueNumbers.remove(3)
print(uniqueNumbers) // Output: Unordered set of numbers

Checking Membership

print(uniqueNumbers.contains(4)) // Output: true

Sets are highly efficient for checking membership compared to arrays.

Creating and Using Enums

An enum (enumeration) defines a type with a fixed set of related values, making code safer and more readable.

Declaring an Enum

enum Weather {
    case sunny, rainy, cloudy, windy
}

Using an Enum

var todayWeather = Weather.sunny

Switch Case with Enums

switch todayWeather {
case .sunny:
    print("It's a bright day!")
case .rainy:
    print("Don't forget an umbrella!")
case .cloudy, .windy:
    print("Mild weather today.")
}

Using Type Annotations

Type annotations explicitly specify the data type of a variable or constant.

Example:

let age: Int = 25
var name: String = "Gati"
var isActive: Bool = true

While Swift can infer types, annotations improve code clarity, especially in functions and complex data structures.

Conclusion

Today, we explored arrays, dictionaries, sets, enums, and type annotations, essential tools for organizing and managing data in Swift. These concepts will help us build robust SwiftUI applications.

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