What does the nil coalescing operator do?

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Main Source: 🔗 Ace the iOS Interview

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TL/DR

We can use the nil coalescing operator ?? to providea default value in an expression involving an Optional. If the Optional resolves to nil, our default value will be used instead.

var username: String?

// Output: Hello, stranger!
print("Hello, \(username ?? "stranger")!")

username = "@aryamansharda"

// Output: Hello, @aryamansharda!
print("Hello, \(username ?? "stranger")!")