The nil Value

nil is Swift's way of saying "there is nothing here at all," like an empty gift box.

In this page:

Only a variable declared with an optional type can be set to nil, representing that it currently holds no value.

Example: Assigning nil

markup

var favoriteColor: String? = "blue"
favoriteColor = nil
print(favoriteColor as Any)

Comparing an optional to nil with == or != is a straightforward way to check whether it currently holds a value.

Example: Checking for nil

markup

var score: Int? = nil
if score == nil {
    print("No score recorded yet")
} else {
    print("Score is \(score!)")
}

Common Mistakes

Trying to assign nil to a non-optional variable; only optional types can ever hold nil.
Assuming nil in Swift behaves like 0 or an empty string; it specifically represents the total absence of a value.
Forgetting that a freshly declared optional without an initial value implicitly starts as nil.

Chapter Summary

nil represents the absence of a value and can only be assigned to optional types.
A non-optional variable can never be nil -- the compiler enforces this at compile time.
An optional declared without an initial value defaults to nil.
Checking if value == nil (or != nil) is a simple way to test for absence.

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