당신은 주제를 찾고 있습니까 “swift escaping closure captures ‘inout’ parameter – iOS : Swift: Capture inout parameter in closures that escape the called function“? 다음 카테고리의 웹사이트 https://chewathai27.com/you 에서 귀하의 모든 질문에 답변해 드립니다: Chewathai27.com/you/blog. 바로 아래에서 답을 찾을 수 있습니다. 작성자 Knowledge Base 이(가) 작성한 기사에는 조회수 13회 및 좋아요 없음 개의 좋아요가 있습니다.
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Swift 3.0 Error: Escaping closures can only capture inout …
I’m getting next error: “Escaping closures can only capture inout parameters explicitly by value”. The problem is inse this function:
Source: stackoverflow.com
Date Published: 4/7/2022
View: 6469
SOLVED: Escaping closure captures ‘inout’ parameter – Swift
I’m trying to get a web page, parse it and return a value extracted from it. I’m getting this error. I don’t really understand what I’m …
Source: www.hackingwithswift.com
Date Published: 12/25/2022
View: 8553
inout paremeter and thread safety | Apple Developer Forums
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.
Source: developer.apple.com
Date Published: 4/9/2022
View: 1329
Swift. Closures – Medium
If a nested escaping closure captures an in-out parameter, Swift throws a compile-time error func someFunction(a: inout Int) -> () -> Int {
Source: medium.com
Date Published: 6/20/2022
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An odd error: “Escaping closure captures mutating ‘self'”
It’s incorrect in theory. According to the Swift language book, a closure is sa to escape a function when the closure is passed as an argument …
Source: forums.swift.org
Date Published: 4/13/2021
View: 7396
Escaping closure captures ‘inout’ parameter …
Escaping closure captures ‘inout’ parameter ‘selectedPassengerId’ in SwiftUI? By admin. April 23, 2022.
Source: getdigitaltech.com
Date Published: 4/18/2021
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swift-evolution/0035-limit-inout-capture.md at main – GitHub
Swift’s behavior when closures capture inout parameters and escape their enclosing context is a common source of confusion. We should disallow implicit …
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Date Published: 3/2/2022
View: 5756
ios – Swift 3.0 Error: Escaping closures can only capture inout …
Using an inout parameter exclusively for an asynchronous task is an abuse of inout – as when calling the function, the caller’s value that …
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Date Published: 4/6/2022
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주제와 관련된 이미지 swift escaping closure captures ‘inout’ parameter
주제와 관련된 더 많은 사진을 참조하십시오 iOS : Swift: Capture inout parameter in closures that escape the called function. 댓글에서 더 많은 관련 이미지를 보거나 필요한 경우 더 많은 관련 기사를 볼 수 있습니다.
주제에 대한 기사 평가 swift escaping closure captures ‘inout’ parameter
- Author: Knowledge Base
- Views: 조회수 13회
- Likes: 좋아요 없음
- Date Published: 2022. 1. 29.
- Video Url link: https://www.youtube.com/watch?v=LiIGNAHRhrM
Swift 3.0 Error: Escaping closures can only capture inout parameters explicitly by value
Using an inout parameter exclusively for an asynchronous task is an abuse of inout – as when calling the function, the caller’s value that is passed into the inout parameter will not be changed.
This is because inout isn’t a pass-by-reference, it’s just a mutable shadow copy of the parameter that’s written back to the caller when the function exits – and because an asynchronous function exits immediately, no changes will be written back.
You can see this in the following Swift 2 example, where an inout parameter is allowed to be captured by an escaping closure:
func foo(inout val: String, completion: (String) -> Void) { dispatch_async(dispatch_get_main_queue()) { val += “foo” completion(val) } }
var str = “bar” foo(&str) { print($0) // barfoo print(str) // bar } print(str) // bar
Because the closure that is passed to dispatch_async escapes the lifetime of the function foo , any changes it makes to val aren’t written back to the caller’s str – the change is only observable from being passed into the completion 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. Instead you have to capture the parameter by copying it, by adding it to the closure’s capture list:
func foo(val: inout String, completion: @escaping (String) -> Void) { DispatchQueue.main.async {[val] in // copies val var val = val // mutable copy of val val += “foo” completion(val) } // mutate val here, otherwise there’s no point in it being inout }
(Edit: Since posting this answer, inout parameters can now be compiled as a pass-by-reference, which can be seen by looking at the SIL or IR emitted. However you are unable to treat them as such due to the fact that there’s no guarantee whatsoever that the caller’s value will remain valid after the function call.)
However, in your case there’s simply no need for an inout . You just need to append the resultant array from your request to the current array of results that you pass to each request.
For example:
SOLVED: Escaping closure captures ‘inout’ parameter – Swift – Hacking with Swift forums
I’m not sure why you’re using an inout parameter here. You should probably be doing something like return a String value or a Result instead. I’m pretty sure inout params aren’t a good fit for async code like this.
Perhaps something like this:
enum PensionError: Error { case malformedURL case badData case dateRegexFailed case invalidPensionDate case differenceError } func getPensionAge(dob: Date, completion: @escaping (Result<(String, Double), PensionError>) -> Void) { let formatter = DateFormatter() formatter.dateFormat = “yyyy-MM-dd” let urlString = “https://www.gov.uk/state-pension-age/y/age/\(formatter.string(from: dob))” guard let url = URL(string: urlString) else { completion(.failure(.malformedURL)) return } URLSession.shared.dataTask(with: url) { (data, response, error) in guard let data = data, let text = String(data: data, encoding: .utf8) else { completion(.failure(.badData)) return } guard let rng = text.range(of: #”State Pension age on *([0-9]* [A-Za-z]* [0-9]*)”#, options: .regularExpression) else { completion(.failure(.dateRegexFailed)) return } let pensionDate = String(text[rng]) .replacingOccurrences(of: “State Pension age on”, with: “”) .trimmingCharacters(in: .whitespacesAndNewlines) formatter.dateFormat = “dd MMM yyyy” guard let dt = formatter.date(from: pensionDate) else { completion(.failure(.invalidPensionDate)) return } let diff = Calendar.current.dateComponents([.day], from: dob, to: dt) guard let daysDiff = diff.day else { completion(.failure(.differenceError)) return } let pensionAge = Double(daysDiff) / 365.25 completion(.success((pensionDate, pensionAge))) }.resume() }
inout paremeter and thread safety
I think it’s important to distinguish between what works on any given implementation and what is defined to work. OOPer’s comments about atomicity, for example, are about implementation, not definition. Let me illustrate this with an example from C (and the reason I’m choosing C, not Swift here, is something I’ll make clear below):
Imagine a memory block like this: static int * b1 = calloc(1, 1024); . Now consider code like this: *b1 += 1 being called from two different threads.
On any given CPU architecture it is very likely that this will produce a result of either 0, 1 or 2, that is, the increments will happen or they won’t. However, according to the C memory model this is undefined and the system (the C compiler and the runtime underneath) is allowed to do whatever it wants in this case. For example:
It could produce 3, or -1.
It could detect the race condition at compile time and fail to compile.
It could detect the race condition at runtime and trap.
It could exploit the fact that this is condition is ‘impossible’ to optimise away the code entirely.
If you’re not already familiar with this sort of thing, you should read the class What Every C Programmer Should Know About Undefined Behavior, part 1, part 2 and part 3.
The problem with talking about concurrency in Swift is that it doesn’t have a well-defined memory model. You can see the beginnings of this start to come together in the Ownership Manifesto, but that’s some way from being done. Thus, it’s very hard to separate implementation from definition because there’s no definition )-:
Note The first step along this path has already been taken, namely SE-0176 Enforce Exclusive Access to Memory. The Concurrency section of that doc will be of interest to you.
The ad hoc guidelines folks typically follow here are:
Incrementing and decrementing reference counts is assumed to be thread safe.
Everything else can be either: Shared between threads if it’s immutable Must be protected from multi-threaded access if it’s mutable
Note The immutable case above is tricky because it’s possible for something to look immutable from the outside but actually be mutable internally. A good example of this is copy-on-write data structures. If you build such a data structure it’s a good idea to design it to be thread safe in this case.
Coming back to your specific problem, it’s hard to offer advice without knowing more about what you’re doing. Specifically, is
aVar
aStruct
aVar
being access be multiple threads simultaneously? If so, this is definitely not safe and you may well crash ifis complex. Your local variable workaround might reduce the incidences of these crashes but it’s still not correct because you still have multiple threads accessing
My general advice for this sort of thing:
Make as much stuff as you can immutable.
For any given mutable value, define a serialisation context (a thread, a serial queue, a mutex) that’s responsible for that value, and only access the value within that context.
Take advantage of function results; I rarely use inout parameters because Swift let’s me return multiple items from a function. Function results are naturally serialised because no one can get at the result until the function is done.
parameters because Swift let’s me return multiple items from a function. Function results are naturally serialised because no one can get at the result until the function is done. Function results make it easier to pass data between contexts. So you can write code like this: let value = someFunction(…) queue.async { mutableValue = value } So all the complex code is within someFunction(…) and, when it’s done, it return the result to the caller when the applies the value from within a serialisation context (in this example I’m assuming a dispatch serial queue).
Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
An odd error: “Escaping closure captures mutating ‘self'”
Hi, I have read SE-0035 and discussions on the net about the error. I think I understand the general cause for the error well. But in my case, the behavior is odd. It may occur or not occur in very similar code. See below.
First, the Counter class is just a utility to reproduce the issue. The key setup is that it has a method which takes a escaping closure.
class Counter { var n: Int = 0 // optional closure is @escaping func increase(action: (() -> Void)? = nil) { n += 1 action?() } func reset() { n = 0 } }
The following code works fine. It doesn’t cause “Escaping closure captures mutating ‘self'” error. This is as expected.
// Example 1 struct WorkingTest { var counter = Counter() func test1() { counter.increase { print(counter.n) } } func test2() { counter.increase { counter.reset() } } } let wt = WorkingTest() wt.test1() wt.test2()
But if I move the code in test1() or test2() to init() , the compiler reports “Escaping closure captures mutating ‘self'” error. Why? And even odder, the code in the closure below doesn’t modify self at all.
// Example 2 struct FailedTest { var counter = Counter() init() { counter.increase { print(counter.n) } } }
While investigating this, I find if I wrap the above problematic code in a function, it works.
// Example 3 struct WorkingTest2 { var counter = Counter() func test1() { counter.increase { print(counter.n) } } func test2() { counter.increase { counter.reset() } } init() { test1() test2() } } let wt2 = WorkingTest2() wt2.test1() wt2.test2()
I’m completely at lost. Why example 2 fails and example 3 works? Thanks for any help!
Escaping closure captures ‘inout’ parameter ‘selectedPassengerId’ in SwiftUI?
[ad_1]I’m attempting to assign worth to property however getting bellow subject.
func buildClassViews(accessibilityID: String, information: Binding<[Passenger]>, selectedPassengerId: inout String) -> [AnyView] { var views: [AnyView] = [] @StateObject var viewModel: ViewModel for ingredient in information { views.append( VStack { HStack { VStack(alignment: .main, spacing: 0) { Textual content(ingredient.fullName.wrappedValue ?? “”) Spacer() } .onAppear(carry out: { selectedPassengerId = “(ingredient.passengerId)” // }) } .convertToAnyView()) } } }
Tried few issues however not getting any clue….undecided what is that this subject and resolve it.
[ad_2]
swift-evolution/0035-limit-inout-capture.md at main · apple/swift-evolution
Limiting inout capture to @noescape contexts
Introduction
Swift’s behavior when closures capture inout parameters and escape their enclosing context is a common source of confusion. We should disallow implicit capture of inout parameters except in @noescape closures.
Swift-evolution thread: only allow capture of inout parameters in @noescape closures
Review
Motivation
Before we had @noescape , we still wanted inout parameters and mutating methods to be usable in closures, without compromising the strong guarantee that an inout parameter can only locally mutate its parameter without callers having to worry about unexpected aliasing or lifetime extension. Since Swift uses closures pervasively for standard library collection operations, and even for assertions and operators like && and || via its @autoclosure feature, it would be extremely limiting if inout parameters could not be captured at all. Dave Abrahams designed our current capture semantics as a compromise: an inout parameter is captured as a shadow copy that is written back to the argument when the callee returns. This allows inout parameters to be captured and mutated with the expected semantics when the closure is called while the inout parameter is active:
func captureAndCall ( inout x : Int ) { let closure = { x += 1 } closure () } var x = 22 captureAndCall ( & x) print (x) // => 23
But this leads to unintuitive results when the closure escapes, since the shadow copy is persisted independently of the original argument:
func captureAndEscape ( inout x : Int ) -> () -> Void { let closure = { x += 1 } return closure } var x = 22 let closure = captureAndEscape ( & x) print (x) // => 22 closure () print ( ” still \( x ) ” ) // => still 22
This change has been a persistent source of confusion and bug reports, and was recently called out in David Ungar’s recent post to the IBM Swift Blog, “Seven Swift Snares & How to Avoid Them”, one in a long line of complaints on the topic.
Proposed solution
I propose we make it so that implicitly capturing an inout parameter into an escapable closure is an error. We added the explicit @noescape annotation in Swift 1.2, and have since adopted it throughout the standard library where appropriate, so the compromise has outlived its usefulness and become a source of confusion.
Detailed design
Capturing an inout parameter, including self in a mutating method, becomes an error in an escapable closure literal, unless the capture is made explicit (and thereby immutable):
func escape ( f : () -> ()) {} func noEscape (@ noescape f : () -> ()) {} func example ( inout x : Int ) { escape { _ = x } // error: closure cannot implicitly capture an inout parameter unless @noescape noEscape { _ = x } // OK, closure is @noescape escape {[x] in _ = x } // OK, immutable capture } struct Foo { mutating func example () { escape { _ = self } // error: closure cannot implicitly capture a mutating self parameter noEscape { _ = self } // OK } }
For nested function declarations, we defer formation of a closure until a reference to the unapplied function is used as a value. If a nested function references inout parameters from its enclosing scope, we disallow references to the nested function that would form an escaping closure:
func exampleWithNested ( inout x : Int ) { func nested () { _ = x } escape (nested) // error: nested function that references an inout cannot be escaped noEscape (nested) // OK }
As an implementation detail, this eliminates the need for a shadow copy to be emitted for inout parameters in case they are referenced by closures. For code that is still accepted after this change, this should not have an observable effect, since a guaranteed optimization pass always removes the shadow copy when it is known not to escape.
Impact on existing code
This will break code that relies on the current inout capture semantics. Some particular legitimate cases that may be affected:
A closure captures the parameter after its local mutations, and never mutates it further or expects to observe mutations from elsewhere. These use cases can explicitly capture the inout parameter immutably using a capture list, which is both more explicit and safer.
The inout parameter is captured by escapable closures that dynamically never execute outside the originating scope, for instance, by referencing the parameter in a lazy sequence adapter that is applied in the immediate scope, or by forking off one or more dispatch_async jobs that access different parts of the parameter but which are synced with the originating scope before it exits. For these use cases, the shadow copy can be made explicit: func foo ( q : dispatch_queue_t, inout x : Int ) { var shadowX = x; defer { x = shadowX } // Operate on shadowX asynchronously instead of the original x dispatch_async (q) { use ( & shadowX) } doOtherStuff () dispatch_sync (q) {} }
For migration, the compiler can offer one of the above fixits, checking the use of the captured inout for mutations after the capture to decide whether an immutable capture or explicit shadow copy is more appropriate. (Or naively, the fixit can just offer the shadow copy fixit.)
This also increases pressure on libraries to make more use of @noescape where possible, as proposed in SE-0012.
Alternatives considered
A possible extension of this proposal is to introduce a new capture kind to ask for shadow copy capture:
func foo ( inout x : Int ) { {[shadowcopy x] in use ( & x) } // strawman syntax }
Swift 3.0 Error: Escaping closures can only capture inout parameters explicitly by value
Using an inout parameter exclusively for an asynchronous task is an abuse of inout – as when calling the function, the caller’s value that is passed into the inout parameter will not be changed.
This is because inout isn’t a pass-by-reference, it’s just a mutable shadow copy of the parameter that’s written back to the caller when the function exits – and because an asynchronous function exits immediately, no changes will be written back.
You can see this in the following Swift 2 example, where an inout parameter is allowed to be captured by an escaping closure:
func foo(inout val: String, completion: (String) -> Void) { dispatch_async(dispatch_get_main_queue()) { val += “foo” completion(val) } }
var str = “bar” foo(&str) { print($0) // barfoo print(str) // bar } print(str) // bar
Because the closure that is passed to dispatch_async escapes the lifetime of the function foo , any changes it makes to val aren’t written back to the caller’s str – the change is only observable from being passed into the completion 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. Instead you have to capture the parameter by copying it, by adding it to the closure’s capture list:
func foo(val: inout String, completion: @escaping (String) -> Void) { DispatchQueue.main.async {[val] in // copies val var val = val // mutable copy of val val += “foo” completion(val) } // mutate val here, otherwise there’s no point in it being inout }
(Edit: Since posting this answer, inout parameters can now be compiled as a pass-by-reference, which can be seen by looking at the SIL or IR emitted. However you are unable to treat them as such due to the fact that there’s no guarantee whatsoever that the caller’s value will remain valid after the function call.)
However, in your case there’s simply no need for an inout . You just need to append the resultant array from your request to the current array of results that you pass to each request.
For example:
키워드에 대한 정보 swift escaping closure captures ‘inout’ parameter
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