结构内部的变异功能

Question

我正在使用Swift 4，我有一个用默认值初始化的结构。我在里面创建了一个函数，它应该读取一个JSON并用它得到的东西改变那些默认值，但它似乎不起作用。

错误：Closure无法隐式捕获变异的self参数

码：

struct Workspace: Decodable {
    var guid: String
    var name: String

private enum CodingKeys : String, CodingKey {
    case guid = "guid"
    case name = "name"
}

init(){
    self.guid = "blbl"
    self.name = "oops"
}

mutating func getUserWorkspace(base: String, completed: @escaping () -> ()){
    let url = URL(string: "some url")!
    var request = URLRequest(url: url)

    request.addValue("Basic \(base)", forHTTPHeaderField: "Authorization")
    request.addValue("application/json", forHTTPHeaderField: "Accept")

    URLSession.shared.dataTask(with: request){ (data, response, error) in
        if error == nil {
            do {
                let res: Workspace = try JSONDecoder().decode(Workspace.self, from: data!)
                self.guid = res.guid  //Error here
                self.name = res.name  //Error here
                DispatchQueue.main.async {
                    completed()
                }
            }catch {
                print ("JSON error")
            }
        }
    }.resume()
}

我改变了让变为var，但我猜还有一些我不明白的东西..

Answer 1

//Try this one and let me know
struct Workspace: Decodable {
    static var shared = Workspace()
    var guid: String
    var name: String

    private enum CodingKeys : String, CodingKey {
        case guid = "guid"
        case name = "name"
    }

    init(){
        self.guid = "blbl"
        self.name = "oops"
    }

    mutating func getUserWorkspace(base: String, completed: @escaping () -> ()){
        let url = URL(string: "some url")!
        var request = URLRequest(url: url)

        request.addValue("Basic \(base)", forHTTPHeaderField: "Authorization")
        request.addValue("application/json", forHTTPHeaderField: "Accept")

        URLSession.shared.dataTask(with: request){ (data, response, error) in
            if error == nil {
                do {
                    let res: Workspace = try JSONDecoder().decode(Workspace.self, from: data!)
                    Workspace.shared.guid = res.guid  //Error here
                    Workspace.shared.name = res.name  //Error here
                    DispatchQueue.main.async {
                        completed()
                    }
                }catch {
                    print ("JSON error")
                }
            }
            }.resume()
    }
}

Answer 2

我建议你使用class而不是struct。无论如何，如果你想使用你的代码，那么在你的变异方法中捕获self，如下所示：

mutating func getUserWorkspace(base: String, completed: @escaping () -> ()){
        let url = URL(string: "some url")!
        var request = URLRequest(url: url)
        var myself = self

        request.addValue("Basic \(base)", forHTTPHeaderField: "Authorization")
        request.addValue("application/json", forHTTPHeaderField: "Accept")

        URLSession.shared.dataTask(with: request){ (data, response, error) in
            if error == nil {
                do {
                    let res: Workspace = try JSONDecoder().decode(Workspace.self, from: data!)
                    myself.guid = res.guid  //Error here
                    myself.name = res.name  //Error here
                    DispatchQueue.main.async {
                        completed()
                    }
                }catch {
                    print ("JSON error")
                }
            }
            }.resume()
  }

Answer 3

我实际上发现了问题..而且它非常愚蠢......我只需要更改函数的“已完成”部分，如下所示：

 mutating func getUserWorkspace(base: String, completed: @escaping (_ arr:[Workspace]?) -> ()){
    let url = URL(string: "SOME URL")!
    var request = URLRequest(url: url)

    request.addValue("Basic \(base)", forHTTPHeaderField: "Authorization")
    request.addValue("application/json", forHTTPHeaderField: "Accept")

    URLSession.shared.dataTask(with: request){ (data, response, error) in
        if error == nil {
            do {
                let rep = try JSONDecoder().decode([Workspace].self, from: data!)
                DispatchQueue.main.async {
                    completed(rep)
                }
            }catch {
                print(error)
            }
        }
    }.resume()
}