Swift Dictionaries: Practical Guide

```html

Working with Swift Dictionaries: A Practical Guide

In Swift, dictionaries are incredibly useful data structures that allow you to store key-value pairs. They offer efficient lookups, updates, and deletions based on unique keys, making them ideal for tasks such as maintaining a collection of settings, counts, or translations.

Basic Dictionary Syntax

A dictionary in Swift is defined using the syntax [KeyType: ValueType]. Both the key and value types can be of any type, but the keys must be hashable.

var capitals: [String: String] = [
        "France": "Paris",
        "Germany": "Berlin",
        "Japan": "Tokyo"
    ]
    

Accessing Values

Accessing a value from a dictionary is done using subscript syntax.

let capitalOfFrance = capitals["France"]
    print(capitalOfFrance)  // Optional("Paris")
    

Note that the result is an optional because the key may not exist in the dictionary.

Modifying Dictionaries

You can add or update a value using subscript notation.

capitals["Italy"] = "Rome"  // Adds a new key-value pair
    capitals["France"] = "Lyon"  // Updates the value for the key "France"
    

To remove a key-value pair, simply set its value to nil.

capitals["Germany"] = nil  // Removes the key-value pair for "Germany"
    

Iterating Over a Dictionary

You can iterate over the key-value pairs of a dictionary using a for-in loop.

for (country, capital) in capitals {
        print("\(country): \(capital)")
    }
    

Checking for Existence

To check whether a key exists in the dictionary, you can use the contains method or check if the value is nil.

if capitals.keys.contains("Japan") {
        print("Capital of Japan is \(capitals["Japan"]!)")
    }
    

Default Values

Using the nil coalescing operator (??), you can provide a default value when accessing a dictionary key.

let capitalOfItaly = capitals["Italy"] ?? "Unknown"
    print(capitalOfItaly)  // "Rome"
    

Conclusion

Dictionaries are a powerful tool in Swift for managing key-value data. By mastering basic operations like creation, modification, and iteration, you can effectively use dictionaries in many common programming scenarios.

```