optional-chaining

问题 As per Apple docs, optional chaining is the following: You specify optional chaining by placing a question mark (?) after the optional value on which you wish to call a property, method or subscript if the optional is non-nil. ... optional chaining fails gracefully when the optional is nil ... My interpretation of this is that a construction as the following is optional chaining: someMasterObject.possiblyNilHandler?.handleTheSituation() ...and that the above line would call the

问题 As per Apple docs, optional chaining is the following: You specify optional chaining by placing a question mark (?) after the optional value on which you wish to call a property, method or subscript if the optional is non-nil. ... optional chaining fails gracefully when the optional is nil ... My interpretation of this is that a construction as the following is optional chaining: someMasterObject.possiblyNilHandler?.handleTheSituation() ...and that the above line would call the

问题 As per Apple docs, optional chaining is the following: You specify optional chaining by placing a question mark (?) after the optional value on which you wish to call a property, method or subscript if the optional is non-nil. ... optional chaining fails gracefully when the optional is nil ... My interpretation of this is that a construction as the following is optional chaining: someMasterObject.possiblyNilHandler?.handleTheSituation() ...and that the above line would call the

问题 Looks like optional chaining has landed. Here's an example What I can't figure out is how to get TS to compile it properly. I'm not getting any syntax errors in my project, but this: let imageFileId = (await db.query(sql`select id from image_files where sha256=${sha256}`))[0]?.id; Is being output as: let imageFileId = (await db.query(mysql3_1.sql `select id from image_files where sha256=${sha256}`))[0]?.id; Which won't run until we get native support in Node. Here's my tsconfig: {

问题 TypeScript 3.7 now supports the optional chaining operator. Hence, you can write code such as: const value = a?.b?.c; I.e., you can use this operator to access properties of an object, where the object itself may be null or undefined . Now what I would like to do is basically the same, but the property names are dynamic: const value = a?[b]?.c; However, there I get a syntax error: error TS1005: ':' expected. What am I doing wrong here? Is this even possible? PS: The proposal seems to imply

问题 Scenario: We're using webpack 4 to create a bundle from our Javascript sources. We're not using Babel because we're authoring only for a single platform (latest Chrome), and we're only using features directly available in Chrome, thus no transpiling is required. The plus side of this is a smaller bundle , and much faster turnaround times while developing. Now we would like to start using the stage 4 optional chaining feature which can be enabled in Chrome using a flag. I've tried to google

问题 When I changed from Objective-C to Swift programming, I have come across ' ! ' (exclamation mark) and ' ? ' (question mark) that often have to be put right after a property , a method call etc. What are these marks used for, and what happens if we did not use them? I searched for a thorough answer on the web but could not find any. So I decided to put here my answer in case for anyone is in search of a clear answer for that. I also included in my answer below a link to a question that is

问题 I am getting this error when running the android project in react react native. This is fresh install of react native version "react": "^16.3.1","react-native": "^0.57.1", It gives error of optional chaining. Can anyone please help me how to enable optional chaining in react native. Loading dependency graph, done. BUNDLE [android, dev] ....../index.js ▓▓▓▓▓▓▓▓▓▓░░░░░░ 64.3% (667/832)::ffff:127.0.0.1 - - [02/Oct/2018:04:30:46 +0000] "GET /index.delta?platform=android&dev=true&minify=false HTTP

问题 When call a function of an object instance, the object may be not exist(optional type), it seems like you can always put an question mark behind the object name, instead of put an exclamation mark behind the object name, and not crash. window!.rootViewController = containerViewController // forced unwrapping // Can change to question mark and not crash. window?.rootViewController = containerViewController // Optional chaining Is that in the place of use forced unwrapping, you can always

问题 This is not allowed (bad expression) if !(let nsDictionaryObject = swiftObject as? NSDictionary) { "Error could not make NSDictionary in \(self)" return } Is it possible to check for the negative of an Optional Chain expression in 1 line? 回答1: In Swift 2.0, you can use guard let nsDictionaryObject = swiftObject as? NSDictionary else { "Error could not make NSDictionary in \(self)" return } This will also bind nsDictionaryObject to the scope outside the guard statement. 回答2: If you are using