A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. werteEintragen () should start after weatherManager. 54. Easiest way is to use the capture list when creating escaping closure, and in that capture list you explicitly capture self as a weak reference: Escaping and Non-Escaping in Swift 3. Swift: Escaping closure captures non-escaping parameter 'onCompletion' 3. You can think of a closure as being a…Capturing closures within closures: Xcode throws error: Escaping closure captures non-escaping parameter. You have to add @escaping to allow them to escape. Hot Network Questions Disclaiming part of an Inheritance What is the `tee` command in Linux?. non-escaping closure — a closure that is called within the function it was passed. Check this: stackoverflow. Their versatility, compact syntax, and powerful capabilities have made them an essential concept to grasp for. Escaping closure captures non-escaping parameter 'completion' (Swift 5) In my project, I came across a situation when I need to use the background queue to create an AVPlayerItem (which I create in setupTrackModels function). async { [weak self] in // process and manipulate. A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. 0. Got the tax refund form. You just have to mark it as so: typealias Action = (@escaping. If you are not storing a reference to it outside of the function, then the only reference to it is the local parameter, which is released as soon as the function exits. Hot Network Questions Print the Christmas alphabetAnd also change the init in the same way and now that the action parameter is actually optional @escaping is no longer needed. However, when I tried to do something like this post, I got these errors: 1. Escaping closure captures non-escaping parameter 'action' Here is my code: I get the error "Escaping closure captures non-escaping parameter 'action'" on lines 2 and 4. Swift: Capture inout parameter in closures that escape the called function. However, we can define two types of closures, i. An escaping closure can cause a strong reference cycle if you use self inside the closure. Escaping closure captures non-escaping parameter. if someone releases a version of their library that has a non-escaping closure and later discovers it needs to be escaping, they can't change it. Hot Network Questions How can I add a circle along the planes? Stellarium and the Taurids How do you deal with movement inertia in an environment after a step?. How to create a closure to use with @escaping. playground:21:47: error: escaping closure captures non-escaping parameter 'finished' URLSession. public struct LoanDetails { public var dueDate: String? public init () {} } public func getLoanDetails (_ result: @escaping (_ loanDetails. startTimer(with: self. October 10, 2016. 0. Basically, escaping will only add in front of a closure, optional is an enum, so it doesn’t make sense to put escaping for an enum. . ; After the loop call notify. Escaping closure captures non-escaping parameter 'promise' 0. data. Hot Network Questions Is it okay if I use a historical figure's name for a work of fiction completely unrelated to history?Capturing closures within closures: Xcode throws error: Escaping closure captures non-escaping parameter. Closure use of non-escaping parameter may allow it to escape. However, we can define two types of closures, i. 在所有者函数返回**之后调用闭包（使用属性）（异步）. if don’t want to. Because dismissScene is a function that accepts a non-escaping closure. @escaping closure gets call even after class deinitialized, But won't it will get nil instance variable if you properly managed memory by using weak self. (you can use Self. addAction method, i. return customerList in searchCustomer happens synchronously when the data (that's obtained asynchronously from getJsonFromAPI) isn't yet available. some case. Passing a non-escaping function parameter 'anotherFunc' to a call to a non-escaping function parameter can allow re-entrant modification of a variable 2. escaping closure captures non-escaping parameter 'resolve'. SWIFT 3 - Convert Integer to Character. But if you make it @escaping, you get error: escaping closure captures mutating 'self' parameter. Jun 8, 2020 at 6:46. The examples below demonstrate how to use without Actually Escaping(_: do:) in conjunction with two common APIs that use escaping closures: lazy collection views and asynchronous operations. Escaping closure captures mutating 'self' parameter, Firebase. I find it confusing that it means a non-escaping closure in the parameter list (which can be overridden with an annotation), an escaping closure in a local variable declaration (which can not be overridden), but even more confusing that the assignment let a = f does define a non-escaping local closure variable. 1. e. g. Since it's a non-escaping closure, it's executed immediately when it's passed to the function. The rule is that an Objective-C nonnullable block is translated into Swift as an @escaping function automatically, unless it is explicitly marked (NS_NOESCAPE ^). updateData on the other hand will fail if the document doesn't exist. Connect and share knowledge within a single location that is structured and easy to search. Any closure that is not explicitly marked as @escaping is non-escaping. May I know why I am getting "Escaping closure captures non-escaping parameter" even the closure is non-escaping? [duplicate] I have the following function static func promptToHandleAutoLink(onEdit: () -> ()) { let alert = UIAlertController(title: nil, message: nil, preferredStyle: . Swift 3. If f takes a non-escaping closure, all is well. 4 Trouble with non-escaping closures in Swift 3. (you can use Self. id, completed: ) and changeVC was called in completed closure, but I wanted to refactor code in which loadDirector only have one parameter. It’s a low level library powering frameworks like Warp and Rocket, as well as the reqwest client library. 1. observeSingleEvent (of:with:) is most likely a value type (a struct ?), in which case a mutating context may not explicitly capture self in an @escaping closure. There are several ways to have a. Escaping closure captures non-escaping parameter 'action' You’re now watching this thread. 弹出 该NSAlert视图 后 (除了 该NSAlert视图 可 进行 选择) 其他 的 视图 不能 进行 操作 ~. Dec 26, 2020 at 18:27. even updating the code base to Swift 4 in Xcode 9, it still has the same issue. As the compiler warns us if we remove self reference:. Also -as mentioned above-, the same behavior would be applicable for the classes and structs:Escaping closure captures non-escaping parameter 'completion' (Swift 5) 0. The resulting. async { completion () } } In this example, the completion closure is marked as escaping, which means it’ll be called after the doSomething. Expression Syntax, Escapinfg and Non escaping Closures, Autoclosures and more. If a closure can escape the function, you’ll need to annotate its function parameter with the @escaping. How to pass parameter to a escaping function that calls escaping function in swift? 0. 在写方法中参数为闭包的回调时，当执行闭包是报错了：Escaping closure captures non-escaping parameter 'failure1'. ). import Foundation func doSomething(completion: @escaping () -> Void) { DispatchQueue. 在这种情况下，如果不. What is different is that the viewModel. Changing this type to a class would likely address your problem. Escaping Closure captures non-escaping parameter dispatch. Closu re use of non - escaping parameter ' xx x' may allow it to escape. And for parameters there is implemented in Swift 3 proposal "Make non-escaping closures the default" :3. Just had to add @escaping to the arguments: @objc func fling(_ options: NSDictionary, resolver resolve: @escaping. actionSheet) alert. This is what we did when we added @escaping so that it can leave the function. Escaping Closures vs. 这个闭包并没有“逃逸 (escape)”到函数体外。. What parameter do you want to pass? Perhaps you could rewrite your question to use simpler and more distinct function names. escaping closure's run time. 52 Escaping. as of Swift 5, or just the type. Fetching JSON, appending to array: Escaping closure captures mutating 'self' parameter. Swift: Escaping closure captures non-escaping parameter 'onCompletion' 5. D oes anyone know how I can solve this? thanks in advance You have. It does not create any breaking change, as long the default rule for optional parameter closures keeps them @escaping. 1. You can set initial values inside init, but then they aren't mutable later. Even if you unwisely find a way to capture a pointer to the place in memory that the self variable is bound to during some specific init call, that value can be moved and/or copied. Promise is also closure, so you need to make it @escaping in arguments as well. Doesn’t cause a reference cycle. When you declare a function that takes a closure as one of its parameters, you can write @escaping before the parameter’s type to indicate that the closure is allowed to escape. 1. Structures and enumerations don’t allow shared mutability, as discussed in Structures and Enumerations Are Value Types. Yoel Jimenez. You can fix this by removing the requirement for self: fn method<'s: 'p>(&self, input: &'s str) -> T;The problem is that escaping/non-escaping isn't enough to express what we want here. If it is nonescaping, changes are seen outside, if it is escaping they are not. Swift 3 :Closure use of non-escaping parameter may allow it to escape. Thus, all generic type argument closures, such as Array and Optional, are escaping. 新版的Swift闭包做参数默认是@noescaping，不再是@escaping。. The closure outlives the function that it is passed into, and this is known as escaping. Swift 3 :Closure use of non-escaping parameter may allow it to escape. You can refer this. Swift 4: Escaping closures can only capture. default). One of the most practical applications of escaping closures is in handling network calls. By writing @escaping before a closure’s parameter type indicates that the closure is allowed to escape (to be called. If you pass a value to a Timer, then the Timer is mutating its own copy of that value, which can't be self. Non-escaping closures have a very clear lifecycle and have become the default closure type in Swift 3 because of it. 0. Hi Swift community, The review of SE-0377: borrow and take parameter ownership modifiers begins now and runs through November 8, 2022. func observe (finished: @escaping ( [Post]) -> Void) { // ALL YOUR CODE. 0. An escaping closure is one that is passed as an argument to a function, but may be called after that function returns. 如果考虑到内存的. This closure never passes the bounds of the function it was passed into. I tried to write an "editor" class that could retain a reference to a property on a different object for later mutation. enum DataFetchResult { case success (data: Data) case failure } protocol DataServiceType { func fetchData (location: String, completion: (DataFetchResult) -> (Void)) func cachedData (location: String) -> Data? } /// An implementation of DataServiceType protocol returning predefined. compiler The Swift compiler in itselfTurns out the problem was in my @escaping closure syntax. Swift ui Escaping closure captures mutating 'self' parameter Hot Network Questions Overvoltage protection with ultra low leakage current for 3. To avoid memory leaks, Swift provides two types of closure: escaping and non-escaping closures. Swift inferring a completion handler closure to be the default @nonescaping instead of @escaping when completion handler explicitly uses @escaping 20 Swift: Escaping closure captures non-escaping parameter 'onCompletion'If you don’t want to escape closure parameters, mark it as @non-escaping. Notice in. Escaping Closures in Swift. Swift @escaping and Completion Handler. First we see on log results. If you knew your closure wouldn’t escape the function body, you could mark the parameter with the @noescape attribute. Capturing closures within closures: Xcode throws error: Escaping closure captures non-escaping parameter. Introduction. Escaping closure captures 'inout' parameter. the closure may modify a captured local variable, or it may it use a network connection. They can if you don't move the captured variables into the closure, i. 1. Escaping Closures in page link. bool1 = true which is changing the value of self. Why do closures require an explicit `self` when they're all non-escaping by default in Swift 3? 55. Learn more here. @escaping 是一个闭包，. (SE-0103) Escaping closure captures non-escaping parameter ‘completion’ The @escaping keyword solves this and explicitly states that the closure can escape: func uploadEscaping(_ fileURL: URL, completion: @escaping -> Void) { /// . I am new to this escape function in Swift, but I follow a tutorial and I use the following function below: (the function is working for me) static func showThreeOptions (messageText: String, titleOne:String, titleTwo: String, actionOne: @escaping () -> (Void), actionTwo:. The type owning your call to FirebaseRef. The concept of Swift Closure is similar to blocks in C. 2. But this would. linkZusammenfuegen () is done. Closures can capture and store references to any constants and variables from the context in which they're defined. In other words, it outlives the function it was passed to. 0. client. addOperation { block (promise. Therefore, a function that takes a function argument where the parameter is both optional and non-escaping cannot be written. I would like to know when I can access the information. A non-escaping closure is simple: It’s passed into a function (or other containing scope), the function/scope executes that closure, and the function returns. The Problem. P. (That's why capture lists exist: to help avoid. closure = c //Error: Non-Ecaping parameter 'c' may only be called } } By setting the closure to a generic type ( T. So, after a function returns, a variable that is passed as &variable will have the modified value In most cases, Swift manages memory…You can use this function to call an API that takes an escaping closure in a way that doesn’t allow the closure to escape in practice. I was trying to understand why the above code is working with the former, but not with the latter. Feb 26, 2020 at 12:08An escaping closure is denoted by the keyword “escaping” before the parameter type in the function definition. Non-escaping closure . Lifecycle of the non-escaping closure: 1. –Since the closure is not marked as @escaping, it is called within the calculateSum function before it returns, allowing us to perform the transformation and sum the values synchronously. Here's my code:However, an escaping closure can’t capture a mutable reference to self when self is an instance of a structure or an enumeration. Closure use of non-escaping parameter may allow it to escape. ; Inside the asynchronous block at the end call leave. I think, to verify that the objective c closure has not escaped, we would store a non-trivial (vs a trivial) closure type in the block (and thereby have the block_descriptor perform copy/destroy_value operations like it does for escaping closures) and check it after the local block copy, that is passed to objective-c, is destroyed. The non-escaping closure passed as the function argument, the closure gets executed with the function’s body and returns the compiler back. I spent lot of time to fix this issue with other solutions unable to make it work. In this case it is meant to add 1 to the score. Basically, @escaping is valid only on closures in function parameter position. @escaping なクロージャはどこかから強参照される可能性があります。 。その参照元をクロージャ. Non-escaping closures on the other hand, cannot be stored and must instead be executed directly when used. fetchImage(internalUrl, task: &task, completion: completion) } SAVE 50% To celebrate Black Friday, all our books and bundles are half price, so you can take your Swift knowledge further without spending big!Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more. So, I have two methods loadHappinessV1 and loadHappinessV2. please elaborate your question more . So that will be all in today’s article, if you. A non-escaping closure A may not be recursively invoked during the execution of a non-escaping closure B which captures the same local variable or inout parameter unless: A is defined within B or. In Swift 1 and 2, closure parameters were escaping by default. Hello Swift community, The review of "SE-0103: Make non-escaping closures the default" begins now and runs through June 27. On LoginViewController file i added a block to performLoginRequest but problem is on LoginManager file. If we don't call @escaping closure at all it doesn't occupy any memory. It is effectively saying someCounter = Counter (someCounter. The sub processes also has @escaping so, they are not the problem. The purpose of including self when using properties inside an escaping closure (whether optional closure or one explicitly marked as @escaping) with reference types is to make the capture semantics explicit. Quote from Swift documentation. 1 Answer. I'd suggest moving asynchronous code like this to an. For most people, most of the time, using a higher level wrapper like these is the right thing to do. If the counter reaches 0 the closure in notify is executed. When you declare a function that takes a closure as one of its parameters, you can write @escaping before the parameter’s type to indicate that the closure is allowed to escape. 1. Regarding non-escaping closures, Apple uses them for most of their built-in higher-order functions (functions that receive one or more functions as parameters and/or. And the second (if provided) must be a UIEvent. Escaping closure captures non-escaping parameter. Casting a closure to its own type also makes the closure escape. (data, response, error) in that "Escaping closure captures non-escaping parameter 'completion". Also, seeing 64 different thread ids does not mean that you had 64 threads running at the same time. That is the cause of the crash. If you intend. Since such closures may be executed at a later time, they need to maintain strong references to all of. Escaping closure captures non-escaping parameter 'completion' – Douglas W. A non-escaping closure is a closure that’s called within the function it was passed into, i. 如果考虑到内存的. 112. How to create a closure to use with @escaping. A non-escaping closure cannot be stored, as it will be executed before the function’s return statement. com/a/46245943/5492956; Escaping Closure: An escaping closure is a closure that’s called after the function it was passed to. Escaping closure captures non-escaping parameter 'finished'. Closure parameters are non-escaping by default, if you wanna escape the closure execution, you have to use @escaping with the closure parameters. You need to pass in a closure that does not escape. A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. Swift differentiates between escaping and non-escaping closures. 5. I didn't provide the capture list and the linker had issues with it, possibly due to a possibility of retain cycle. This worked. 0. Also capture by strong reference if you purposefully want to extend the life of your object for the sake of the closure and you know that the closure will be executed and disposed of. As you may know, closure parameters, by default, cannot escape. Check this: stackoverflow. The usage of DispatchGroup is very easy. This is because operation as () -> Void is a "rather complex" expression producing a value of type () -> Void . A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. But that means that the situation is exactly the same as the second one (the one with var); the compiler has to think about how anotherClosure is storing a closure (the curly braces) which captures the incoming parameter clsr, and it comes to exactly the same conclusion as in the previous example, for exactly the same reasons. Summary. Implicit self in @escaping Closures when Reference Cycles are Unlikely to Occur Swift 5. In Swift, closures are non-escaping by default. extension OperationQueue { func publisher<Output, Failure: Error>. In Swift 3, inout parameters are no longer allowed to be captured by @escaping closures, which eliminates the confusion of expecting a pass-by-reference. owner函数将这个闭包保存在属性中. If you’ve opted in to email or web notifications, you’ll be notified when there’s activity. It was he who suggested I post here on the Swift Forum, I've posted a link to this thread into the Apple. However, you’re not allowed to let that inout parameter escape. When you. The problem manifests itself when you supply the flags. Hot Network QuestionsEscaping Closure captures non-escaping parameter dispatch. You can't create a sender that takes a completion block. In Swift, a closure is a self-contained block of code that can be passed to and called from a function. Prior to Swift 3 (specifically the build that ships with Xcode 8 beta 6), they would default to being escaping – you would have to mark them @noescape in order to prevent them from being stored or captured, which guarantees they won't outlive. The function runs the closure (or not) The function returns. Non-escaping closures passed in as arguments are guaranteed to not stick around once the function returns. But if you make it @escaping, you get error: escaping closure captures mutating 'self' parameter. Either you can move it in a method, or even simpler, sth like this:Just pass in a closure as parameter of checkSubscription() and call it when your verification code is completed. Xcode throws error: Escaping closure captures non-escaping parameter. When you declare a function that takes a closure as one of its parameters, you can write @escaping before the parameter’s type to indicate that the closure is allowed to escape. If you need to hold onto that closure after the function it was passed into returns, you'll need to mark the closure with the keyword @escaping. x, by default closure parameter was @escaping which means that closure can be escape during the function body execution. This worked. Non-escaping closures passed in as arguments are guaranteed to not stick. Bad idea. This is known as closing over those constants. To resolve it, you need to tell the system that you are aware of this, and warn the caller, by adding @escaping. How to create a closure to use with @escaping. id > $1. S. ~~. Hot. Hot Network Questions Which real world computers are the workstations shown at the Daily Planet in the DCAU show Superman: The Animated Series based on?Closure use of non-escaping parameter may allow it to escape. 3 VAll optional closures must be escaping, since the closure is stored inside the Optional. However, it’s impossible to create a reference cycle with a non-escaping closure — the compiler can guarantee that the closure will have released all objects it captured by the. x, Apple made a change: closure parameters became @non-escaping by default. How to create a closure to use with @escaping. を付ける必要があります。 循環参照に気をつける. The problem has nothing to do with the closure, or static, or private. When you declare a function that takes a closure as one of its parameters, you can write @escaping before the parameter’s type to indicate that the closure is allowed to. e. Non-Escaping Closures. data = data DispatchQueue. That is the closure is not. They are particularly useful for…The selector must take either zero, one, or two parameters and those parameters can only be very specific parameters. it is executed immediately upon receipt), it is in no danger of capturing self in some tricky way and causing a retain cycle. Closure use of non-escaping parameter - Swift 3 issue. I'd like do it in getTracks. For local variables, non-contexted closures are escaping by default. – Tom. By Ole Begemann. One thing to keep in mind when using non-escaping closures is that you need to be careful about capturing variables and resources from the surrounding context. If the document doesn't exist, setData (with or without merge) will create the document. Capture Lists. 55 Escaping Closures in Swift. Instead, the closure is saved and can be executed later, even after the function or method has returned. Is you don't actually need any instance variables then make doCoolStuff () a static function and you will no longer need to call it with self. First, the token provider doesn't match our signature ((@escaping (Result<Token, Error>) -> Void) -> Void). A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. Escaping closure captures mutating 'self' parameter, Firebase 2 Implicit self in @escaping Closures when Reference Cycles are Unlikely to Occur Swift 5. x and Swift 2. 2. DispatchQueue. func loadData(){ LoadXZYAPI() { [weak self] (data:Any?) in guard let strongSelf = self else { return } strongSelf. try func queryForParams(completion: @escaping queryCompletionBlock) Share. Hello Hyper! For those not familiar, Hyper is an HTTP implementation for Rust, built on top of Tokio. Closure parameters are non-escaping by default. If a closure can escape the function, you’ll need to annotate its function parameter with the @escaping. 1 Answer. In your example getRequest has @escaping closure completionHandler and struct foo tries to modify itself inside this closure implementation. So, when you call . Learn more about TeamsProperties in a struct like this (View) are immutable. Another thing is, closure is non escaping by default in function as parameters, but something like enum associate value, struct, etc, are escaping by default. Swift 3 :Closure use of non-escaping parameter may allow it to escape. 原因和解决 逃逸 闭 包 前面没 有 加@ escaping 关键字 ，加上就可以了，如下图 参考连接 stack overflow 官方文档： Escaping Closures「escaping」属性とは？ まず @escaping 属性について説明します。 関数の引数として渡すクロージャに @escaping を付けると、そのクロージャが関数のスコープ外で保持できるようになります。 関数からエスケープするので「escaping」と命名されたのだと思います。Playground execution failed: error: Swift - Draft. If you remove that, the problem goes away. A non-escaping closure is simple: It’s passed into a function (or other containing scope), the function/scope executes that closure, and the function returns. 将闭包传递给函数. For instance, you can define a nested function (either using func or using a closure expression) and safely mutate an inout parameter. Escaping Closure captures non-escaping parameter dispatch. In this example, the performOperation function takes a closure as an argument. When you assign a closure to a property, you are assigning a reference to that closure. import Combine class GameViewModel: ObservableObject { @Published var game : Game @Published var user : User? init (game: Game) { self. I create similar function that contains same parameter with nonEscapingClosure. This rendition of _syncHelper is called when you supply flags and it’s not empty. An escaping closure is a closure that is called after the function it was passed to returns. error: Converting non-escaping parameter 'completionHandler' to generic parameter 'Element' may allow it to escape By Definition: "A non escaping closure goes out of the scope and stops existing in memory as soon as the function body gets executed. 函数执行闭包（或不执行）. swift Parameter is implicitly non-escaping. In Swift 3, it’s the other way around: closure parameters are non-escaping by default. shared. 在 Swift 1 和 2中， closure by default 是 escaping的，所以我们需要用 @noescape 来mark. Right now I use DispatchQueue and let it wait two seconds. This explains why you can't modify an inout parameter in an escaping closure. global (). Escaping closure captures non-escaping parameter 'function' Xcode says. 4 Closure use of non-escaping parameter - Swift 3 issue. In Swift, closures are non-escaping by default. Instead you have to capture the parameter by copying it, by adding it to the closure's capture list : A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. e. Uploads the file asynchronous DispatchQueue. 函数返回. Maybe that's not important to the rest of your argument (I stopped reading because GAT's are kinda over my head), but I wanted to point this out. Closure use of non-escaping parameter may allow it to escape. parameter, result: result) } } As you've probably noticed, this will cause a memory leak, since onSuccess is an escaping closure and it's retaining self. Looks like 64 is the size of your list. With RevenueCat Paywalls you can customize native, remotely configurable paywall templates and optimize them with Experiments. 1. ModalResponse. 前2项 (按钮)——点击第1项 ('确定')/第2项 ('取消')/后NSAlert视图会消失并打印 NSApplication. In this example, the closure captures a weak reference to self using a capture list. Swift does not run in sequence. The rule for when you need @escaping is simple – if a closure function argument can escape the lifetime of the function call, it needs to be marked as @escaping (the compiler simply won't let you compile it otherwise). The inner () -> Void is not marked @escaping. But when I try the code , it says Escaping closure. Closure use of non-escaping parameter - Swift 3 issue. In Swift, closures are non-escaping by default and they are: Non-storable. Store value from escaping closure. 0. It is the completion handler inside the dataCompletionHandler that I do not. So. " but we are using this inside the function In Swift 3, inout parameters are no longer allowed to be captured by @escaping closures, which eliminates the confusion of expecting a pass-by-reference. Preventing Retain Cycle. 0. Now, if localClosure was escaping in some way, I'd understand this error, but it doesn't escape. In your case you are modifying the value of self. He also suggest we investigate changing the default language rule for optional parameter closures. My first attempt was to call resolve and reject inside the closure: import . An example of non-escaping closures is when using. 问题 2 . I understand that the definition of escaping closures is If a closure is passed as an argument to a function and it is invoked after the function returns, the closure is escaping. Unfortunately, in your example where you pass result in searchLocation(keyword: completion:), the compiler is erroring with "Passing non-escaping parameter 'result' to function expecting an @escaping closure", which I can't seem to work around. 在 Swift 1 和 2中， closure by default 是 escaping的，所以我们需要用 @noescape 来mark. I'd like do it in getTracks function, and this method must also have a completion handler which I need to call in main.