Highlighting an important, yet probably overlooked, instance method on NSDictionary where the key starts with '@'

NSDictionaryValueForWhat.swift

import UIKit

var dictionary = NSMutableDictionary()

let key = "@123"
dictionary[key] = "Test Value"
let value = dictionary[key] // Test Value

let newKey = "@4321"
dictionary[newKey] = "New Test Value"

let newValue = dictionary.value(forKey: newKey)