不能在约束为具体类型的通用协议上调用自定义init方法

Question

我正在尝试编写一个CollectionDataAdapter，如下所示：

public protocol InitializableCell {
    associatedtype T

    init(item: T)
}

public typealias ACCollectionNodeCellAction = (_ collectionNode: ASCollectionNode, _ indexPath: IndexPath, _ object: Any) -> Void

open class ASCollectionNodeAdapter<Provider: CollectionDataProvider, Cell: ASCellNode>:
    NSObject,
    ASCollectionDataSource,
    ASCollectionDelegate
    where Cell: InitializableCell, Provider.T == Cell.T
{
    // MARK: - Delegates
    public var didSelectCell: ACCollectionNodeCellAction?

    // MARK: - Private Properties
    let provider: Provider
    let collectionNode: ASCollectionNode

    // MARK: - Lifecycle
    init(collectionNode: ASCollectionNode, provider: Provider) {
        self.collectionNode = collectionNode
        self.provider = provider
        super.init()
        setUp()
    }

    func setUp() {
        collectionNode.dataSource = self
        collectionNode.delegate = self
    }

    // MARK: - ASCollectionDataSource

    public func numberOfSections(in collectionNode: ASCollectionNode) -> Int {
        return provider.numberOfSections()
    }

    public func collectionNode(_ collectionNode: ASCollectionNode, numberOfItemsInSection section: Int) -> Int {
        return provider.numberOfItems(in: section)
    }

    public func collectionNode(_ collectionNode: ASCollectionNode, nodeBlockForItemAt indexPath: IndexPath) -> ASCellNodeBlock {
        return { [weak self] () -> ASCellNode in

            guard let `self` = self, let item = self.provider.item(at: indexPath) else {
                return ASCellNode()
            }
            return Cell.init(item: item)


        }
    }

    // MARK: - ASCollectionDelegate
}

问题是我无法初始化类型ASCellNode的Cell并且符合InitializableCell说：

  

参数标签'（item :)'与任何可用的重载都不匹配

如果我这样调用init：Cell(item: item)编译器抱怨：

  

非标称类型'Cell'不支持显式初始化

怎么回事？因为Cell已经符合InitializableCell协议