“生成器”不是“Self.SubSequence”的成员类型

Question

我正在尝试将下面的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样的印象。

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，我在行中得到了上述错误，let generator: AnyGenerator<Array<SubSequence.Generator.Element>> = anyGenerator {。我想不出怎么解决这个问题。

Answer 1

有几个问题：

• 在Swift 3中，Generator被重命名为Iterator，因此AnyGenerator重命名为AnyIterator。
• IndexDistance是Collection的关联类型，它表示索引之间的步骤数。
• 在Swift 3中，“集合移动他们的索引”，参见关于Swift进化的一种新的馆藏与指数模型。

综合起来，您的方法在Swift 3中可以这样看：

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

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

Collection方法，用于索引的提升。

当然，您可以使用while循环而不是Iterator实现相同的结果。

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
    }
}