将 if 语句更改为 guard 会引发此错误。条件绑定的初始化程序必须具有可选类型，而不是“(Bool, String)”

Question

我想将以下 if 语句更改为 guards。这样做会引发以下错误条件绑定的初始化程序必须具有可选类型，而不是“(Bool, String)” 知道我应该怎么做吗？任何帮助将不胜感激。谢谢

dispatch_async(backgroundQueue, {
            let (success, errmsg) = client.connect(timeout: 5)
            print("Connected",success)
            if success {
                let (success, errmsg) = client.send(str: self.jsonString)
                print("sent",success)

                if success {
                    let data = client.read(ApplicationConfig.expectedByteLength)
                    if let d = data {
                        if let recievedMsg = String(bytes: d, encoding: NSUTF8StringEncoding){
                            print(recievedMsg)
                            let (success, errormsg) = client.close()
                        }
                    }
                }else {
                    print("Message not sent", errmsg)
                }

            }
        })

    }

Answer 1

因为你声明的变量没有 ?（非可选）并且还给它默认值所以 guard 假设它永远不会 nil 这就是你得到错误的原因，你仍然可以像这样使用 guard guard let object: Type = data else {...}

Answer 2

听起来您可能正在将 if 语句转换为 guard let 语句，这需要可选类型。

你应该可以直接使用 guard 类似的东西：

    dispatch_async(backgroundQueue, {
        let (success, errmsg) = client.connect(timeout: 5)
        print("Connected",success)
        guard success else {
            return
        }

        let (success, errmsg) = client.send(str: self.jsonString)
        print("sent",success)

        guard success else {
            print("Message not sent", errmsg)
            return
        }

        let data = client.read(ApplicationConfig.expectedByteLength)
        guard let d = data else {
            return
        }
        guard let recievedMsg = String(bytes: d, encoding: NSUTF8StringEncoding) else {
            return
        }

        print(recievedMsg)
        let (success, errormsg) = client.close()
    })

注意：这实际上并没有编译，因为代码试图重新定义 success 和 errormsg 常量，但它应该为您提供总体思路。

将 if 语句更改为 guard 会引发此错误。条件绑定的初始化程序必须具有可选类型，而不是“(Bool, String)”

Changing an if statement to guard throws this error. Initializer for conditional binding must have Optional type, not '(Bool, String)'

guard

ios

swift