swift中的编译器错误indexOf（）

Question

所以我有这样的功能：

    var localIndices: [ChartHighlight] = []

    for globalHighlight in globalIndices
    {
        if let globalSet = data?.dataSets[globalHighlight.dataSetIndex]
        {
            if globalSet.dynamicType === dataSetType
            {
                let chartData = getChartData(dataSetType)

                if (chartData == nil)
                {
                    return globalIndices
                }

                let localdataSetIndex = chartData!.dataSets.indexOf(globalSet)
                if (localdataSetIndex != nil)
                {
                    localIndices.append(ChartHighlight(xIndex: globalHighlight.xIndex, dataSetIndex: localdataSetIndex!, stackIndex: globalHighlight.stackIndex))
                }
            }
            else
            {
                return globalIndices
            }
        }
    }

编译器抱怨

let localdataSetIndex = chartData!.dataSets.indexOf(globalSet)

说

  

无法转换类型＆＃39; IChartDataSet＆＃39;的值预期参数类型＆＃39; @noescape（IChartDataSet）抛出 - ＆gt;布尔＆＃39;

我很困惑为什么我不能将indexOf()用于[IChartDataSet]。这与chartData!.dataSets是[IChartDataset]而IChartDataset是protocol类型相关吗？ 我没有看到swift doc提到这个，或者我错过了它......

Answer 1

要将indexOf方法与元素一起用作输入参数，dataSets的元素类型IChartDataSet必须符合Equatable协议，如{{1}所示扩展名定义：

CollectionType

或者您可以改为使用谓词闭包：

    extension CollectionType where Generator.Element : Equatable {
       /// Returns the first index where `value` appears in `self` or `nil` if
        /// `value` is not found.
        ///
        /// - Complexity: O(`self.count`).
        @warn_unused_result
        public func indexOf(element: Self.Generator.Element) -> Self.Index?
    }