Closure cannot implicitly capture self parameter. Swift

Question

I've got an error "Closure cannot implicitly capture self parameter". Tell me please how it fix?

struct RepoJson {
...
    static func get(url: String, completion: @escaping (RepoJson!) -> ()) {
        ...
    }
} 

struct UsersJson {
    var repo: RepoJson!
    init() throws {   
        RepoJson.get(url: rep["url"] as! String) { (results:RepoJson?) in
            self.repo = results //error here
        }
   }
}

Possible duplicate of Closure cannot implicitly capture a mutating self paramter — Moriya
– Moriya, Commented Jun 24, 2017 at 9:55

farzadshbfn · Accepted Answer · 2017-06-24 09:50:26Z

12

It's because you're using struct. Since structs are value, they are copied (with COW-CopyOnWrite) inside the closure for your usage. It's obvious now that copied properties are copied by "let" hence you can not change them. If you want to change local variables with callback you have to use class. And beware to capture self weakly ([weak self] in) to avoid retain-cycles.

answered Jun 24, 2017 at 9:50

farzadshbfn

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8 Comments

Yurii Petrov Over a year ago

I use a class, it's work well but I've got a new problem. RepoJson.get(url: rep["url"] as! String) { (results:RepoJson?) in if let repoData = results { self.repo = repoData } } self.repo did get value, here well. But when I print array repo equals nil.

farzadshbfn Over a year ago

Do you print it right after you initialize the class? Because repo is going to be filled after callback returns value.

Yurii Petrov Over a year ago

I create button and press it's and always equals nil.

farzadshbfn Over a year ago

p.s: The way you're setting self.repo = repoData, it causes memory-leak because you captured self strongly. If you are 100% sure that this class is available when your callback returns, use it like this { [unowned self] repoData in self.repo = repoData } but it seems to me that your use-case can not guarantee that UsersJson is available when callback returns hence use this: { [unowned self] repoData in self?.repo = repoData }

farzadshbfn Over a year ago

Usually this scenarios need time, because there is a network call and it's gonna take some time. print it with a delay like (1 or 2 seconds) data will be available.

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