Feed Collection Container Example

Container.swift

// MARK: - Data

protocol FeedItem {
}

struct ShareFeedItem: FeedItem {
    let id: String
}

// MARK: - Delegates

/// Abstract common protocol for all CollectionDelegates
protocol FeedItemCollectionDelegate {
    func canHandle(_ item: FeedItem) -> Bool
    
    func cellForRow(indexPath: IndexPath, item: FeedItem) -> UIView
}

/// Typed collection delegate type.
protocol FeedTypedItemCollectionDelegate {
    associatedtype Item: FeedItem
    
    var cellsForRegistration: [UIView.Type] { get }
    
    func cell(at indexPath: IndexPath, for item: Item) -> UIView
}

extension FeedTypedItemCollectionDelegate {
    func wrapInAdapter() -> CollectionAdapter<Self> {
        CollectionAdapter(delegate: self)
    }
}

// MARK: - Real implementation

class FeedShareCollectionDelegate: FeedTypedItemCollectionDelegate {
    var cellsForRegistration: [UIView.Type] = [
        UILabel.self
    ]
    
    func cell(at indexPath: IndexPath, for item: ShareFeedItem) -> UIView {
        return UILabel()
    }
}

// MARK: - Adapter implementation

struct CollectionAdapter<Delegate: FeedTypedItemCollectionDelegate>: FeedItemCollectionDelegate {
    
    let delegate: Delegate
    
    func canHandle(_ item: FeedItem) -> Bool {
        item is Delegate.Item
    }
    
    func cellForRow(indexPath: IndexPath, item: FeedItem) -> UIView {
        guard let typedItem = item as? Delegate.Item else {
            preconditionFailure("Item \(item) cannot be cast to \(Delegate.Item.self)")
        }
        return delegate.cell(at: indexPath, for: typedItem)
    }
}

// MARK: - Usage in container

class Container {
    var delegates: [FeedItemCollectionDelegate] = [
        FeedShareCollectionDelegate()
            .wrapInAdapter()
    ]

    var feedItems: [FeedItem] = [
        ShareFeedItem(id: "foo"),
        ShareFeedItem(id: "bar")
    ]

    func cellForRow(indexPath: IndexPath) -> UIView {
        let item = feedItems[indexPath.item]
        for delegate in delegates where delegate.canHandle(item) {
            return delegate.cellForRow(indexPath: indexPath, item: item)
        }
        preconditionFailure("Can't find FeedItemCollectionDelegate for \(item)")
    }
}