找不到成员<方法名称>对于 Swift 中的结构类型 [英] Could not find member <method name> for struct type in Swift

问题描述

我有以下代码，但是当我尝试使用以下 x.initial(2).flatten() 进行链接时，出现编译错误，提示 Could not find member flatten

I have the following code but when I try to chain using the following x.initial(2).flatten() I get a compile error saying Could not find member flatten

我做错了什么.为了确保我可以继续链接，我在每个链接的方法(例如 flatten、initial 等)之后返回 self.

What am I doing wrong. To make sure I can keep chaining I am returning self after each chained method such as flatten, initial, etc.

struct $ {

    var resultArray: AnyObject[] = []
    init(array: AnyObject[]) {
        self.resultArray = array
    }

    mutating func first() -> AnyObject? {
        return $.first(self.resultArray)
    }

    mutating func flatten() -> $ {
        self.resultArray = $.flatten(self.resultArray)
        return self
    }

    static func first(array: AnyObject[]) -> AnyObject? {
        if array.isEmpty {
            return nil
        } else {
            return array[0]
        }
    }

    mutating func initial() -> $ {
        return self.initial(1)
    }

    mutating func initial(numElements: Int) -> $ {
        self.resultArray = $.initial(self.resultArray, numElements: numElements)
        return self
    }

    func value() -> AnyObject[] {
        return self.resultArray
    }

    static func flatten(array: AnyObject[]) -> AnyObject[] {
        var resultArr: AnyObject[] = []
        for elem : AnyObject in array {
            if let val = elem as? AnyObject[] {
                resultArr += self.flatten(val)
            } else {
                resultArr += elem
            }
        }
        return resultArr
    }

    static func initial(array: AnyObject[]) -> AnyObject[] {
        return self.initial(array, numElements: 1)
    }

    static func initial(array: AnyObject[], numElements: Int) -> AnyObject[] {
        var result: AnyObject[] = []
        for (index, _) in enumerate((0..array.count - numElements)) {
            result += array[index]
        }
        return result
    }

}

var x = $(array: [[1, 2], 3, [[4]]])
var y = x.initial(2).flatten() //Throws the error

推荐答案

这是因为 initial 返回了 $ 的不可变实例.然后，您尝试对其调用变异方法 (flatten).为了再次改变它，你必须将它存储在另一个可以改变的变量中.您也可以将其更改为 class 而不是 struct，因为类是可变的.

It is because initial returns an immutable instance of $. You are then trying to call a mutating method (flatten) on it. In order to mutate it again, you will have to store it in another variable that can be mutated. You could also change it to be a class instead of a struct because classes are mutable.

注意目前，您收到的错误消息很糟糕，但这就是目前 Swift 的生活.

Note currently, the error message you are getting is terrible, but that is life with Swift at the moment.

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