ArrayType在扩展where子句中

Question

extension Array where Element: _ArrayType, Element.Generator.Element: Any {
    func transpose() -> [Element] {
        if self.isEmpty { return [Element]() }
        let count = self[0].count
        var out = [Element](repeating: Element(), count: count)
        for outer in self {
            for (index, inner) in outer.enumerated() {
                out[index].append(inner)
            }
        }
        return out
    }
}

从Swift 2.2转换后，我在Swift 3.0中收到此错误。数组的元素也是数组。那么如何在Swift 3.0中定义呢？

Answer 1

extension Array where Element : Collection, Element.Index == Int, Element.IndexDistance == Int {
    func transpose() -> [[Element.Iterator.Element]] {
        typealias InnerElement = Element.Iterator.Element
        if self.isEmpty { return [] }
        let count = self[0].count
        var out = [[InnerElement]](repeating: [InnerElement](), count: count)
        for outer in self {
            for (index, inner) in outer.enumerated() {
                out[index].append(inner)
            }
        }
        return out
    }
}