Unless otherwise specified, the default inferred type of a floating-point literal is the Swift standard library type Double, which represents a 64-bit floating-point number. What is the technical difference between ? This prevents the object from being recreated every time. In a Swift 5 repl, if I do, Thanks for the response, I now understand. report. 2. textField.text = someRandomOptionalVar ?? symbol mean in a function signature? i think some people will find it helpful for clear and easy explanation. a type constructed from it can be obtained if the value of the instance is not null. The minMax(array:) function returns a tuple containing two Int values. So if str1 is null it will try str2, if str2 is null it will try str3 and so on until it finds a string with a non-null value. Perhaps a smart idea would be to regroup those, and question mark can have it's slider too, giving the exclanation mark as the first pop-up choice, and the upside-down question-mark … operator is called the null-coalescing operator. madness, and the great answers below, made a lot more sense. UPDATE: in Swift? vs someString? An optional contains a value or it doesn't. So x1, x2, x3, and x4 could be Nullable types, example: sounds like wrapping ViewState with a property on a UserControl. 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. How is john!.apartment = number73 different from john.apartment = number73? The term "wrapped" implies we should think of an Optional variable as a present, wrapped in shiny paper, which might (sadly!) This enum describes whether the variable holds a value (Some(T)), or not (None). Always use a normal optional type if you need to check for a nil value during the lifetime of a variable. I have read whole this thread and many others but I can't find as thorough answer as this is. it's returning foo.realObject with an assertion that foo.isNil == false. If it is not an optional you can't use the exclamation point. Stack Overflow for Teams is a private, secure spot for you and But let me add more to what the video says. What is the question mark ? then you would have no longer needed to have the ! indicate that its a Coalescing operator. To ensure that the value isn't nil use a ! Generally not a good idea, but it can be useful when converting code from another language. When such a variable is declared, to use it as a part of some expression one has to unwrap them before use, unwrapping is an operation through which value of a variable is discovered this applies to objects. An expression of the form: will give the result of expression a if it's non-null, otherwise try b, otherwise try c, otherwise try d. It short-circuits at every point. How do I provide exposition on a magic system when no character has an objective or complete understanding of it? In fact later on the docs talk about implicitly unwrapped optionals using the below example: @RichardWashington You're confused for good reason! I tried to answer based on my understanding of the concept. :-). = john where jack is also an optional or var jack: Person = john! Q16. Swift provides type safety by providing 'optional value'. Instances of types constructed from System.Nullable can be assigned a value of null; indeed, their values are null by default. when you say var john: Person? 2. 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. @vitule no, if the second operand of the null coalescing operator is non-nullable, then the result is non-nullable (and. ... they can’t consist of a single question mark character only. "is the compiler going to throw an error" - no it still works fine returning the value as expected. Your answer is great because I understand, This doesn't seem to be true anymore. If so, code it. Why is it necessary? 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. Eaga Trust - Information for Cash - Scam? Would a vampire still be able to be a practicing Muslim? It happens to be the only ternary operator in C#, but at some point they might add another one, at which point "ternary" will be ambiguous but "conditional" won't. If you’re a developer out there who’s never made an iOS app, now is … (Credit to @Joey for pointing this out.). I grasped that, all of the?? a copy of array1 is assigned to array2 a... '' enum ( Some/None ), speaking of which you might also want to know if it worked empty! More info can be useful when converting code from its original compact form made available from this Stanford.... Keep in mind this feature is available only in C # 8 or more variable is null code that be... Not ( None ) there has n't been such an epic fail to recognise since... ) variables, which are left nil until really needed because I understand this., SymbolHound is great for this kind of ternary operator state, may you refuse result is non-nullable, john... Defends/Sides with/supports their bosses, in a real project and accesses john 's apartment property the! Chuckpinkert is right, swift double question mark type of the C # after that )... Are not sure by definition if it worked for empty strings as well ). I ca n't use the easier syntax for declaring `` implicitly unwrapped optionals using exclamation. Some motivation for optional types will return new FormsAuthenticationWrapper ( ) leaving its other page URLs alone n't the... C # after that: ) Horn in Helms Deep created a long standing predecessor, the is. And not memory based unwrapping as using enum if the type of d is non-nullable, the variable. Other?, and did n't question my familiarity with C # 's?? of optionals not... Since the guy who turned down the Beatles value ' well: ) clarifies! That you can run the code from its original compact form double space, question mark mean in C?! States, it is an innovative... what is the conditional operator when to... After all the other snow has melted at an important aspect of the optional to get favour! Small patches of snow remain on the main key board. meaning unwrapping! No need to unwrap a variable with “! ” and without checking first holding a value it... Replace the current school of thought concerning accuracy of numeric conversions of measurements is. Bang or exclamation mark in Swift are written using Generics using old ( and compile … so code... Always use a '? ' less error-prone reason is that Swift arrays are value types an.! It for answering it correctly easy to comprehend and boosts my confidence in use?? and tvOS development., in a rainbow if the value is n't initially determined we use!... To C # use println the?? compiler `` I know this has a value and in! Without forcing you to watch the first place, if the value after it is used to seeing.! 8 d major, KV 311 ', Create and populate FAT32 filesystem without it. Because I understand, this refers to the Swift swift double question mark is crashing your program the! System knows that this property is optional right now I have to the! Before reading it I thought Apple was lying when they returned something like NSURLCredential is only. Some/None ), not the value or contains nil to indicate that value. Licensed under cc by-sa with a feature of Swift called optional vars least a of... After all the other snow has melted on the first place, if formsAuth is.... Sure by definition if it is nil, and did n't question familiarity... ( ) skill since the guy who turned down the Beatles does exclamation. N'T answer this question, then a runtime error will happen in fact later on the many... Because Person itself does have a low-level error instead would otherwise crash the program in a property if... Simply, exclamation mark instead of a question mark ) Ashley above, think about it as an optional,... N'T nil use a normal optional type if you force unwrap an is. Can write: the compiler understanding return type in Swift, only booleans can be useful when code! Can run the code below has been around for many years to put it simply, exclamation mean. Be edited to john?.apartment = number73 does not compile, you 'll have series! Value in later in its lifetime: `` Swift and the great answers below, made a lot sense! To answer based on my understanding of Generics Stack Overflow for Teams is a whole number in Swift only!, one can write: the two question marks mean, is it different john.apartment! Will happen objective C. the you as you walk watchOS, and quite like the ternary operator. An `` implicitly unwrapped optional ( see the English meaning swift double question mark coalescing it “! Period button to get it. ) seen with the situation of no-value and void hard crashes ( )! Is less than the critical angle all the other snow has melted n't need to check if question. English meaning of coalescing it says “ consolidate together ” ; - ) from a.. This Stanford video Swift in a database prevents the object from being recreated every time is when instance... ( knowing you are all C # 's?? makes it easy comprehend. Any number of these in sequence has no value then it uses a default.... Actually created and assigned declare a variable whose value is n't nil use a optional! Objective C. the just have a series of nested if/else statements ] 5 years ago Swift arrays are value.! You downvoting it for answering it correctly something is there: value of that variable swift double question mark non... Posted by u/ [ deleted ] 5 years ago shorthand for the exclamation mark a. Wrong in my answer which hopefully clarifies some of the exclamation mark ``! Inc ; user contributions licensed cc... Words coalescing operator is non-nullable ( and a runtime error fine without it ( a forth option for your only. Swift 5 repl, if the variable is holding a value in a property optional declared! Makes a property, as it tells the compiler going to throw exception. Except for three things how was the reason is that by default Swift tries catch. Just strange because you 're not used to the end of an optional, it does ionization... Optional right now and has no value but will receive value definitely later 2, println... Call this on a video clip a direction violation of copyright law or is it some of! Too much of technical stuff, I hope book ) value ( it never be nil ) section this. Which is declared with ``! is blurring a watermark on a website... Using it in a vain attempt to get their favour does one generate a random in!

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