Swift 为什么可以用这种奇怪的方式编写UICollectionViewDiffableDataSource初始值设定项？

在通过保罗·哈德逊学习斯威夫特时，我遇到了一些奇怪的事情

UICollectionViewDiffableDataSource的初始值设定项定义为：

public init(collectionView: UICollectionView, cellProvider: @escaping UICollectionViewDiffableDataSource<SectionIdentifierType, ItemIdentifierType>.CellProvider)

public init（collectionView:UICollectionView，cellProvider:@escaping UICollectionViewDiffableDataSource.cellProvider）

据我所知，没有其他初始值设定项。但是，Paul成功地将其初始化如下，省去了cellProvider参数：

dataSource = UICollectionViewDiffableDataSource<Section, App>(collectionView: collectionView) { collectionView, indexPath, app in
    switch self.sections[indexPath.section].type {
    case "mediumTable":
        return self.configure(MediumTableCell.self, with: app, for: indexPath)
    case "smallTable":
        return self.configure(SmallTableCell.self, with: app, for: indexPath)
    default:
        return self.configure(FeaturedCell.self, with: app, for: indexPath)
    }
}

dataSource=UICollectionViewDiffableDataSource（collectionView:collectionView）{collectionView，indexPath，应用程序在
开关self.sections[indexPath.section].type{
案例“中表”：
返回self.configure（MediumTableCell.self，with:app，for:indexPath）
案例“smallTable”：
返回self.configure（SmallTableCell.self，with:app，for:indexPath）
违约：
返回self.configure（FeaturedCell.self，with:app，for:indexPath）
}
}

与此同时，Ray Wenderlich's会这样做：

dataSource = UICollectionViewDiffableDataSource<Section, App>(collectionView: collectionView, cellProvider: { (collectionView, indexPath, app) -> UICollectionViewCell? in
    switch self.sections[indexPath.section].type {
    case "mediumTable":
        return self.configure(MediumTableCell.self, with: app, for: indexPath)
    case "smallTable":
        return self.configure(SmallTableCell.self, with: app, for: indexPath)
    default:
        return self.configure(FeaturedCell.self, with: app, for: indexPath)
    }
})

dataSource=UICollectionViewDiffableDataSource（collectionView:collectionView，cellProvider:{（collectionView，indexPath，app）->UICollectionViewCell？在
开关self.sections[indexPath.section].type{
案例“中表”：
返回self.configure（MediumTableCell.self，with:app，for:indexPath）
案例“smallTable”：
返回self.configure（SmallTableCell.self，with:app，for:indexPath）
违约：
返回self.configure（FeaturedCell.self，with:app，for:indexPath）
}
})

---

我试图理解保罗的方式背后到底是什么样的快速“魔法”，因为他似乎放弃了手机提供商的争论，而是做了一些时髦的了结。他在这里究竟应用了哪些Swift规则？

在您的案例中，您可以看到两种方法，可以使用不同的语法编写相同的规则

在这里，您将以预期的方式使用所有参数，包括两个参数collectionView和cellProvider

dataSource = UICollectionViewDiffableDataSource<Section, App>(collectionView: collectionView, cellProvider: { (collectionView, indexPath, app) -> UICollectionViewCell? in
    switch self.sections[indexPath.section].type {
    case "mediumTable":
        return self.configure(MediumTableCell.self, with: app, for: indexPath)
    case "smallTable":
        return self.configure(SmallTableCell.self, with: app, for: indexPath)
    default:
        return self.configure(FeaturedCell.self, with: app, for: indexPath)
    }
})

---

关于or的更多信息

感谢所有为我指明正确方向的人。查看更多更简明的示例可能会有所帮助：

{ collectionView, indexPath, app in
    switch self.sections[indexPath.section].type {
    case "mediumTable":
        return self.configure(MediumTableCell.self, with: app, for: indexPath)
    case "smallTable":
        return self.configure(SmallTableCell.self, with: app, for: indexPath)
    default:
        return self.configure(FeaturedCell.self, with: app, for: indexPath)
    }

func executeThis(info: String, completion: ((String) -> Void)) {
    completion(info)
}

let completion: ((String) -> Void) = { value in 
    print("Done: " + value)
}

// Pass the closure variable to the completion param:
executeThis(info:"Some Activity", completion:completion)

// Provide the closure directly as an argument:
executeThis(info:"Some Activity 2", completion: { value in
    print("Done: " + value)
})

// Trailing closure: the last param, which is a closure, is implicitly provided via "{ value in"
executeThis(info:"Some Activity 3") { value in
    print("Trailing closure done: " + value)
}

---

我建议您阅读Swift指南。干得好。还有一件小事，从完成闭包中删除分号。：）

func executeThis(info: String, completion: ((String) -> Void)) {
    completion(info)
}

let completion: ((String) -> Void) = { value in 
    print("Done: " + value)
}

// Pass the closure variable to the completion param:
executeThis(info:"Some Activity", completion:completion)

// Provide the closure directly as an argument:
executeThis(info:"Some Activity 2", completion: { value in
    print("Done: " + value)
})

// Trailing closure: the last param, which is a closure, is implicitly provided via "{ value in"
executeThis(info:"Some Activity 3") { value in
    print("Trailing closure done: " + value)
}