Optional Property

The default of any IF statement is to check if something is true. So for example, your code "if batteries { println("Batteries included") } can be read as "If batteries is TRUE then println "Batteries included", but you have no handle for if it is false.

If you were to rewrite your code to handle a case where batteries is false, it would look like this:

let toy = Electronic(title: "RC Car", price: 79) 
toy.batteries = false 
if let batteries = toy.batteries { 
     if batteries{
          println("Batteries included.")
     } else {
          println("Batteries not included.")
     }
}

The else statement will handle all cases where batteries is not true.

if argument is false it does not execute the code inside if statement. Very purpose of if statement is that execute the code if it is true otherwise leave it there and jump after if statement.