Dictionary default values
If you try to read a value from a dictionary using a key that doesn’t exist, Swift will send you back nil – nothing at all. While this might be what you want, there’s an alternative: we can provide the dictionary with a default value to use if we request a missing key.
To demonstrate this, let’s create a dictionary of favorite ice creams for two people:
let favoriteIceCream = [
"Paul": "Chocolate",
"Sophie": "Vanilla"
]We can read Paul’s favorite ice cream like this:
favoriteIceCream["Paul"]But if we tried reading the favorite ice cream for Charlotte, we’d get back nil, meaning that Swift doesn’t have a value for that key:
favoriteIceCream["Charlotte"]We can fix this by giving the dictionary a default value of “Unknown”, so that when no ice cream is found for Charlotte we get back “Unknown” rather than nil:
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