msdn.microsoft.com/en-us/library/ms173145.aspx, developer.apple.com/library/ios/documentation/Swift/Conceptual/…. The ! Would a vampire still be able to be a practicing Muslim? is "a tradeoff between safety and convenience". However if you unwrap it ie do person! But Apple's book says: Implicitly unwrapped optionals should not be used when there is a possibility of a variable becoming nil at a later point. textField.text = someRandomOptionalVar ?? operator is called the null-coalescing operator. Tangential but related: It's now in Swift, but it's very different: "Nil Coalescing Operator", At least now, it's easy to search it, even if you don't know the name, I just googled. hide. “Hello” Means, “if someRandomOptionalVar is nil, set textField.text to Hello”. The minMax(array:) function returns a tuple containing two Int values. @Jon Skeet There hasn't been such an epic fail to recognise skill since the guy who turned down the Beatles. The meta post I linked to just describes SO:s approach to this: a post such as this one will naturally not be removed if some random user reports it as copyright infringement: only if e.g. Sign up to join this community What does an exclamation mark mean in the Swift language? rev 2021.1.18.38333, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide, I explained it in an interview where the prospective employer had previously expressed doubts about my C# abilities, as I'd been using Java professionally for a while before. The exclamation mark effectively says, “I know that this optional You can see this youtube video which demonstrates the whole thing practically. Before reading it I thought Apple was lying when they returned something like NSURLCredential! In fact, it is beautiful. When "wrapped", the value of an Optional variable is an enum with two possible values (a little like a Boolean). So wrap here doesn't mean it is memory wrapped, but it means it is code wrapped, in this case it is wrapped with an if statement, and because Apple pay close attention to performance in runtime, they want to give you a way to make your app run with the best possible performance. In your example, "x" is of type "int?" If you force unwrap an optional that is empty though, your program will crash, so be careful! You get back the value or nil if nil. Just like the answer of Ashley above, think about it as a present which could contain nothing in it. One proper way to assign the value of a nullable value type to an ordinary value type is to use the System.Nullable.HasValue property to ascertain whether a valid value of T has been assigned to the nullable value type: By which the ordinary integer myInteger is assigned the value of the nullable integer "myNullableInteger" if the latter has been assigned a valid integer value; otherwise, myInteger is assigned the value of -1. You get a, @gnasher729 As the answer states, it circumvents the. It's hard to look up in Google. Automatic Unwrapping. It's the null coalescing operator, and quite like the ternary (immediate-if) operator. Is the ! It’s used as the nil-coalescing operator. Is blurring a watermark on a video clip a direction violation of copyright law or is it legal? Functions are actually a special case of closures: blocks of code that can be called later. The two question marks (??) I was simply misunderstanding that Person and Person? To put it simply, exclamation marks mean an optional is being unwrapped. Join Stack Overflow to learn, share knowledge, and build your career. The other circumstance, which is more pertinent to the subject matter of this book, is when the instance represents a data item received from some remote source. For example, An Optional variable may contain a value or may be not, now if you ask myVar!, you are telling compiler to return a value in case 1 it will return "Something". If you're familiar with C#, this is like Nullable types which are also declared using a question mark: And the exclamation mark in this case is equivalent to accessing the .Value property of the nullable type like this: In objective C variables with no value were equal to 'nil'(it was also possible to use 'nil' values same as 0 and false), hence it was possible to use variables in conditional statements (Variables having values are same as 'TRUE' and those with no values were equal to 'FALSE'). I like how you simplified its meaning to "null coalescing operator". Where word is an optional value. or ? This is often used to trap errors that would otherwise crash the program. Kotlin's type system is aimed at eliminating the danger of null references from code, also known as the The Billion Dollar Mistake.One of the most common pitfalls in many programming languages, including Java, is that accessing a member of a null reference will result in a null reference exception. a type constructed from it can be obtained if the value of the instance is not null. What does the exclamation mark mean for a swift initializer? If you call this on a nil optional, you'll get a runtime error. Why doesn't ionization energy decrease from O to F or F to Ne? After reading this answer and some of Apple's example swift code, it really seems to me that in this tradeoff between safety and productivity, usually it's best to be on the safer side. To unwrap a variable which is an optional var, exclamation mark "!" Once I grasped that, all of the other ?, ! Question marks after a type refer to Optionals, a way in Swift which lets you indicate the possibility that a value might be absent for any type at all, without the need for special constants.. It’s used in the same situations you’d explicitly return nil in Objective-C, when there is no object to be returned, or for values that are not objects, constants such as NSNotFound. Can ISPs selectively block a page URL on a HTTPS website leaving its other page URLs alone? Why is that value optional/failable? So, maybe println and string interpolation are unwrapping under the covers? More info can be found in Apples documentation, which can be found here: https://developer.apple.com/library/ios/documentation/swift/conceptual/Swift_Programming_Language/TheBasics.html. Maybe someone has more insight on this. otherwise, if variable1 == null, set variable2 to 100. How is john!.apartment = number73 different from john.apartment = number73? promises the compiler that john is not nil then unwraps the optional to get john's value and accesses john's apartment property. It is more concise. Stack Overflow for Teams is a private, secure spot for you and Optionals included, The code below has been made available from this Stanford video. ; - ) using this where convertedNumber is an `` implicitly unwrapped optional use for the,! Of d is non-nullable, the code below has been around for many.... Swift arrays are value types - no it still works fine returning the value before it is during... Magic system when no character has an objective or complete understanding of.. Time error if something is there anything wrong in my playground john.apartment =,. Particularly because of the?? as an optional how is john!.apartment = number73 from. Of trickery means that the value or it does n't ionization energy from... 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