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Mastering Swift 5.3
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When we declare variables in Swift, they are by default non-optional, which means that they must contain a valid, non-nil value. If we try to set a non-optional variable to nil
, it will result in an error.
For example, the following code will throw an error when we attempt to set the message
variable to nil
because it is a non-optional type:
var message: String = "My String"
message = nil
It is very important to understand that nil
in Swift is very different from nil
in Objective-C or other C-based languages. In these languages, nil
is a pointer to a non-existent object; however, in Swift, a nil
value is the absence of a value. Grasping this concept is very important in order to fully understand optionals in Swift.
A variable defined as an optional can contain a valid value, or it can indicate the absence of a value. We indicate the absence of a value by assigning it a special nil
value. Optionals of any type can be set to nil
, whereas...