Question

我试图将下面的Swift 2扩展方法转换为Swift 3。

extension CollectionType {

    func chunk(withDistance distance: Index.Distance) -> [[SubSequence.Generator.Element]] {
        var index = startIndex
        let generator: AnyGenerator<Array<SubSequence.Generator.Element>> = anyGenerator {
            defer { index = index.advancedBy(distance, limit: self.endIndex) }
            return index != self.endIndex ? Array(self[index ..< index.advancedBy(distance, limit: self.endIndex)]) : nil
        }
        return Array(generator)
    }

}

Xcode转换工具给我留下了这个。

extension Collection {

    func chunk(withDistance distance: Int) -> [[SubSequence.Iterator.Element]] {
        var index = startIndex
        let generator: AnyGenerator<Array<SubSequence.Generator.Element>> = anyGenerator {
            defer { index = index.advancedBy(distance, limit: self.endIndex) }
            return index != self.endIndex ? Array(self[index ..< index.advancedBy(distance, limit: self.endIndex)]) : nil
        }
        return Array(generator)
    }

}

现在我在行let generator: AnyGenerator<Array<SubSequence.Generator.Element>> = anyGenerator {处收到了上述错误。我无法弄清楚如何解决这个问题。

Answer 1

有几个问题：

Generator已在Swift 3中重命名为Iterator，因此 AnyGenerator至AnyIterator。
IndexDistance是Collection的关联类型表示索引之间的步数。
在Swift 3中，＆＃34;集合移动他们的索引＆＃34;，请参阅关于斯威夫特进化的A New Model for Collections and Indices。

总而言之，您的方法可以像这样在Swift 3中查找：

extension Collection {

    func chunk(withDistance distance: IndexDistance) -> [[SubSequence.Iterator.Element]] {
        var pos = startIndex
        let iterator: AnyIterator<Array<SubSequence.Iterator.Element>> = AnyIterator {
            // Already at the end?
            if pos == self.endIndex { return nil }

            // Compute `pos + distance`, but not beyond `self.endIndex`:
            let endPos = self.index(pos, offsetBy: distance, limitedBy: self.endIndex) ?? self.endIndex

            // Return chunk and advance `pos`:
            defer { pos = endPos }
            return Array(self[pos..<endPos])
        }
        return Array(iterator)
    }
}

let a = [1, 2, 3, 4, 5, 6, 7]
let c = a.chunk(withDistance: 2)
print(c) // [[1, 2], [3, 4], [5, 6], [7]]

我已将本地index变量重命名为pos，以避免与

混淆

public func index(_ i: Self.Index, offsetBy n: Self.IndexDistance, limitedBy limit: Self.Index) -> Self.Index?

用于推进索引的Collection方法。

当然，您可以使用while循环获得相同的结果而不是Iterator：

extension Collection {

    func chunk(withDistance distance: IndexDistance) -> [[SubSequence.Iterator.Element]] {
        var result: [[SubSequence.Iterator.Element]] = []
        var pos = startIndex
        while pos != endIndex {
            let endPos = self.index(pos, offsetBy: distance, limitedBy: self.endIndex) ?? self.endIndex
            result.append(Array(self[pos..<endPos]))
            pos = endPos
        }
        return result
    }
}

＆＃39;发电机＆＃39;不属于Self.SubSequence＆＃39;的成员类型。

1 个答案: