由于Stride类型，无法符合RandomAccessCollection

Question

我试图制作一个包装另一个的集合，并将固定大小的子集合作为元素出售：

struct PartitionedCollection<C: RandomAccessCollection>: BidirectionalCollection {

    typealias TargetCollection = C

    let collection: C
    let wholePartitionCount: C.IndexDistance
    let stragglerPartitionCount: C.IndexDistance
    let span: C.IndexDistance

    init(on c: C, splittingEvery stride: C.IndexDistance) {
        let (q, r) = c.count.quotientAndRemainder(dividingBy: stride)
        collection = c
        wholePartitionCount = q
        stragglerPartitionCount = r.signum()
        span = stride
    }

    var startIndex: C.IndexDistance {
        return 0
    }
    var endIndex: C.IndexDistance {
        return wholePartitionCount + stragglerPartitionCount
    }

    subscript(i: C.IndexDistance) -> C.SubSequence {
        // If `C` was only a Collection, calls to `index` would be O(n) operations instead of O(1).
        let subStartIndex = collection.index(collection.startIndex, offsetBy: i * span)
        if let subEndIndex = collection.index(subStartIndex, offsetBy: span, limitedBy: collection.endIndex) {
            return collection[subStartIndex ..< subEndIndex]
        } else {
            return collection[subStartIndex...]
        }
    }

    func index(after i: C.IndexDistance) -> C.IndexDistance {
        return i.advanced(by: +1)
    }

    func index(before i: C.IndexDistance) -> C.IndexDistance {
        return i.advanced(by: -1)
    }

}

似乎我可以将其设为RandomAccessCollection。我更改了基本协议，并且操场编译器抱怨该类型不符合Collection，BidirectionalCollection和RandomAccessCollection。我得到了最后一个的Fix-It存根。编译器添加3个副本：

var indices: CountableRange<C.IndexDistance>

在我删除其中两个副本之前，所有副本都标记为：

Type 'C.IndexDistance.Stride' does not conform to protocol 'SignedInteger'

即使我填写了该属性，我也会保留错误：

var indices: CountableRange<C.IndexDistance> {
    return startIndex ..< endIndex
}

我认为C.IndexDistance是Int，它是自己的Stride，应符合SignedInteger。发生了什么事？我可以为indices定义不同的类型吗？我应该定义一些其他成员以获得随机访问（以及哪些和如何）？

我尝试添加index(_:offsetBy:)和distance(from:to:)方法;没有帮助。我尝试将indices更改为Range<C.IndexDistance>;它也没有帮助，它使编译器拒绝将类型视为BidirectionalCollection和RandomAccessCollection。