swift - 在 swift indexOf() 中获取编译器错误

Question

所以我有一个这样的函数:

    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
            }
        }
    }

编译器报错在

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

这样说

Cannot convert value of type 'IChartDataSet' to expected argument type '@noescape (IChartDataSet) throws -> Bool'

我很困惑为什么我不能为 [IChartDataSet] 使用正常的 indexOf()。这与 chartData!.dataSets 是 [IChartDataset] 而 IChartDataset 是 protocol 类型有关吗？我没有看到 swift 文档提到这个或者我错过了它......

Answer 1

要使用 indexOf 方法并将元素作为输入参数，您的 dataSets 元素类型 IChartDataSet 必须符合 Equatable 协议(protocol)，您可以从 CollectionType 扩展定义中看到:

    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?
    }

或者您可以改用谓词闭包:

let localdataSetIndex = chartData!.dataSets.indexOf { $0 === globalSet }