A dictionary in Swift is a list of key-value pairs separated by colons and surrounded by square brackets such as [key: value]. Values returned from a dictionary are optional because the key may not exist in the dictionary.
// A dictionary literal
let d = ["one": 1, "two": 2, "three": 3]
// An empty dictionary
var e: [String: Int] = [:]
// Get a value from a dictionary
var fruits = ["apples": 1, "oranges": 3]
print(fruits["oranges"])
// Prints an optional 3
// Add an item to a dictionary
fruits["berries": 8]
print(fruits)
// Prints a dictionary containing ["apples": 1, "oranges": 3, "berries": 8]
