ios - Swift Array 将 nil 的 var 传递给 .contains 和 .filter 时会发生什么

Question

我正在尝试理解我正在从事的项目中的一些代码。我有一个字符串数组属性:变量名称:[String]!

func findName(name: String?) -> [Name]? {
    if name != nil {
        return nameManager.namesForSearchString(name)?.filter({self.names.contains($0.name)})
    } else { 
        return nameManager.allNames.filter({self.names.contains($0.name)}) //<-what get's returned here?
    }
}

我不明白的是，如果名称​​是 nil，调用 .contains 时会发生什么，那个，会发生什么调用 .filter 时会发生什么？这是在 Favorites 类中实现的，如果点击按钮，我需要调用此函数以返回所有收藏夹，那么我将传递给此函数的内容以确保 Names: [Name] 被返回？

在较低的层次上，我想了解 .contains 和 .filter 是如何工作的，以及如果将 nil 传递给它们会返回什么。

来自不同提交的相同方法的另一个版本(我也没有写)是这样的:

func findFavorites(name: String?) -> [Station]? {
        if name != nil {
            return nameManager.namesForSearchString(name)!.filter({contains(self.names, $0.objectId)})
        } else {
            return nameManager.allNames.filter({contains(self.names, $0.objectId)})
        }
    }

Answer 1

我不想发布一个没有答案的帖子，但我确实希望它的格式正确，所以我想评论是行不通的。这可能会帮助您了解发生了什么，以及过滤器/包含会发生什么。如果您还有任何问题，请告诉我，我会回答问题。如果我完全偏离基地，也请告诉我!

    // I don't know why this is implicitely unwrapped, as a nil in this Array crashes Playground execution
var localNames: [String!] = ["Troy", "Bob", "Donald"]

// I'm just modelling what I know about NameManager
struct NameManager {
  var allNames = [Name(name: "Bob"), Name(name: "Liz"), Name(name: "Anastasia")]
}

// I also assume the `name` in Name is a non-optional.
struct Name {
  var name: String = "some name"
}

var nameManager = NameManager()

func findName(name: String?) -> [Name]? {
  // Case where `name` is non-nil is excluded for demonstration purposes
  // I have expanded all the closure short-hands so we always see what we're doing.
  let allNames = nameManager.allNames
  // namesMatchingName is of type [Name], that we get by applying a filter.
  // `filter` works on a predicate basis: it goes through each element, one at a time,
  // and checks if it meets the "predicate", that is, a boolean 
  // condition that returns true or false. If it DOES meet the criteria, it will be included in
  let namesMatchingName = allNames.filter { (currentName) -> Bool in
    // Now we're inside the filter-predicate. What we do here is check if the `currentName`
    // is in `localNames`.
    let namesHasCurrentName = localNames.contains(currentName.name)
    // If the name IS in `localNames` we return true to the filter, 
    // which means it will be included in the final array, `namesMatchingName`.
    return namesHasCurrentName
  }
  // So now we have all the names that appear in both `nameManager.allNames` and `localNames`
  return namesMatchingName
}

findName(nil) // returns [{name: "Bob"}]