Swift Tutorial - Swift Optionals

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If you can't be sure a variable has a value present, you can use optionals.

An optional is a variable that can have either an assigned value or no value at all.

Using optionals is an alternative to setting objects to nil .

Optionals can be used with any type in Swift including numbers, strings, and objects.

You declare optionals like variables or constants, but you must include a ? after the type declaration.

Like variables and constants, the data type of an optional may be inferred.

The following code shows how to declare String Optional.

var s:String?

The variable s in the code above is declared as an optional, and the starting value is nil.

Forced Unwrapping

If you are sure that an optional has a value, then you can use an exclamation point !! to unwrap the value.

For instance, if you know that s has a value, then you could unwrap s and use the value as follows.

var s:String?
s = "ABC"
println(s!)

Attempt to unwrap an optional that has no value, you will get a runtime error.

We need to test your optional with an if statement before attempting to unwrap the optional.

The following code shows how to test an optional Before Unwrapping Optionals.

if s{
    "The value of s is "
    s!
}else{
    "No value in s"
}

Optional Bindings

Optional bindings tests an optional and unwraps the optional in an if statement.

The following code shows how to use Optional Bindings.

var s:String?
s = "ABC"
println(s!)

if let myString = s{
    "The value of s is "
    myString
}else{
    "No value in s"
}

The code above has a constant declaration right after the if statement so that you are testing for nil and assigning a temporary constant in the code block if a value is present.

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