Working with Dictionaries in Swift: Basics and Operations

A portrait painting style image of a pirate holding an iPhone.

by The Captain

May 23, 2024

Working with Dictionaries in Swift

Dictionaries are a fundamental data structure in Swift that allow you to store key-value pairs. This tutorial will cover how to work with dictionaries in Swift, including declaring, accessing, modifying, and iterating over dictionaries.

Declaring a Dictionary

In Swift, you can declare a dictionary using the following syntax:

var studentGrades = ["Alice": 95, "Bob": 87, "Charlie": 92]}

This declares a dictionary `studentGrades` with keys "Alice", "Bob", and "Charlie" mapping to their respective integer values.

Accessing and Modifying Values

You can access and modify values in a dictionary using subscript notation:

// Accessing values
let aliceGrade = studentGrades["Alice"]

// Modifying values
studentGrades["Bob"] = 90}

Iterating Over a Dictionary

To iterate over a dictionary, you can use a for-in loop with key-value pairs:

for (name, grade) in studentGrades {
    print("\(name) has a grade of \(grade)")

Checking for Key Existence

You can use the `contains` method to check if a key exists in a dictionary:

if studentGrades.contains(where: { $0.key == "Alice" }) {
    print("Alice's grade is present in the dictionary")


In this tutorial, we covered the basics of working with dictionaries in Swift, including declaring, accessing, modifying, iterating, and checking for key existence. Dictionaries are a powerful tool for mapping keys to values and are commonly used in Swift programming.