我试图在 Swift中构建一个数据结构,将Integer映射到一个对象数组(一个字典,其中int为键,数组为value).对象非常小,它们只需包装UIColor和Int.我有两个实现,一个使用Swift数组作为Dictionary的值类型,而另一个使用NSMutableArray作为值类型.我的Objective-C代码执行速度非常快,但我的Swift代码运行得非常慢.理想情况下,我不想使用NSMutableArray,并希望将其保留为Swift数组.原因是我正在编写算法和性能问题,我注意到了objC_msgSend的一些开销.任何人都可以帮我优化我的Swift代码吗？我做错了什么,或者这只是快速处理数组作为值类型的副产品？如果是,我想理解为什么值类型在这种情况下表现得如此之慢,我的选择是什么,以及这种情况如何能够在未来扩展？下面我发布了一个代码段和结果基准：

Swift数组代码：

let numColors = colorCount(filter: filter,colorInfoCount: colorInfo.count)
var colorCountsArray: [Int] = [Int]()
var countToColorMap: [Int:[CountedColor]] = [Int:[CountedColor]](minimumCapacity: capacity)
var topColors = [CountedColor]()

var startTime = CACurrentMediaTime()
for (color,colorCount) in colorInfo {
    colorCountsArray.append(colorCount)
    if countToColorMap[colorCount] != nil {
        countToColorMap[colorCount]?.append(CountedColor(color: color,colorCount: colorCount))
    } else {
        countToColorMap[colorCount] = [CountedColor(color: color,colorCount: colorCount)]
    }
}
var endTime = CACurrentMediaTime()
print("Time after mapping: \(endTime - startTime)")

迅捷表现：

Time after mapping: 45.0881789259997

NSMutableArray代码：

let numColors = colorCount(filter: filter,colorInfoCount: colorInfo.count)
var colorCountsArray: [Int] = [Int]()
var countToColorMap: [Int:NSMutableArray] = [Int:NSMutableArray](minimumCapacity: capacity)
var topColors = [CountedColor]()


var startTime = CACurrentMediaTime()
for (color,colorCount) in colorInfo {
    colorCountsArray.append(colorCount)
    if countToColorMap[colorCount] != nil {
        countToColorMap[colorCount]?.add(CountedColor(color: color,colorCount: colorCount))
    } else {
        countToColorMap[colorCount] = NSMutableArray(object: CountedColor(color: color,colorCount: colorCount))
    }
}
var endTime = CACurrentMediaTime()
print("Time after mapping: \(endTime - startTime)")

NSMutableArray表现：

Time after mapping: 0.367132211999888

colorInfo对象是将UIColor对象映射到表示计数的Integer值的字典.代码本质上反向映射,将整数映射到UIColor数组(它是一个数组,因为多个颜色可以具有相同的计数). colorInfo里面有60,000个UIColor,Int键值对.

countToColorMap[colorCount]?.append(CountedColor(color: color as! UIColor,colorCount: colorCount))

if countToColorMap[colorCount] != nil {
    countToColorMap[colorCount]?.append(CountedColor(color: color as! UIColor,colorCount: colorCount))
} else {
    countToColorMap[colorCount] = [CountedColor(color: color as! UIColor,colorCount: colorCount)]
}

Elapsed Time: 74.2517465990022
53217

var countForColor = countToColorMap.removeValue(forKey: colorCount) ?? []
countForColor.append(CountedColor(color: color as! UIColor,colorCount: colorCount))
countToColorMap[colorCount] = countForColor

Elapsed Time: 0.370953808000195
53217