The factorial of a number is the product of all the positive integers up to that number. Let’s take as an example a common programming exercise: a function to calculate the factorial of an integer.
#DOWNCAST ONLY UNWRAPS OPTIONALS CODE#
Indeed many bugs exist because developers usually write code with this assumption. In an ideal world, our code always works on complete and well defined data. What is the point of having optionals in Swift? When a value cannot be initialized: failable initializers Optionals in structures and classes: optional chainingĪvoiding the checks for nil: implicitly unwrapped optionalsĪsking an object for its type: downcasting Using optional values: forced unwrapping, optional binding and nil coalescing Why do we need optionals in the first place? I have written a more comprehensive guide on Swift optionals that you can find here. This guide was written for the first version of Swift. Then I will talk about what problems they solve, why they are a good idea and how they enforce good practices and better code (in my opinion). I am going to first have a look at what optionals are and how they to use them. Besides this, the operators for optionals (?, !, and ?) cause confusion because they have different meanings in different context. Although I sort of understood what they meant, in many places I did not really know why I was doing something or if it was the correct way or not.Įspecially if you are new to programming, it might be hard to see what problems optionals solve or when to use them. Question and exclamation marks would pop up here and there, leaving me puzzled on the why. My first approach was to just try and use them in my current project, but that did not go well. The cause was that I didn’t take the required time to fully understand them. I have to admit that at the beginning it took me a while too to wrap my mind around them. If either of them is nil, the code inside the if block will not be executed, and the code in the else block will be executed instead.Since the introduction of Swift, optionals seem to have used a lot of confusion for people learning the language. In this example, both message and favoriteNumber are unwrapped and assigned to new, non-optional constants message and favoriteNumber, respectively. Print("message: \(message), favoriteNumber: \(favoriteNumber)") // Output: message: Hello there!, favoriteNumber: 42 You can use optional binding to unwrap multiple optionals at once: let message: String? = "Hello there!" Print(message) // Output: Hello, optional binding! Shadow Variable Namesīecause naming things is so hard, it’s common practice to give the unwrapped constant the same name as the optional (thereby shadowing that optional): let message: String? = "Hello, optional binding!" It’s important to note that when using optional binding, the unwrapped value is only available within the scope of the if statement, or the else statement if the optional was nil. If possibleString is nil, the code inside the if block will not be executed, and the code in the else block will be executed instead. In this example, the optional possibleString is safely unwrapped and assigned to a new, non-optional constant definiteString if it contains a value. Print(definiteString) // Output: Hello, optional binding! Here’s an example of using optional binding to safely unwrap an optional string: let possibleString: String? = "Hello, optional binding!" Optional binding is a safe way to unwrap optionals, allowing you to check if a value exists before using it.
However, in order to use the value inside an optional, it must be unwrapped. Use the force unwrapped form, as, only when you are sure the downcast will. In Swift, optionals represent the possibility of a value being absent. To unwrap an optional is to use one of several procedures to access the.
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