Creating custom query functions with key paths

, , Swift , . , , key paths, function/result builders . ., Swift .

, , , , . - «-DSL», , .

key paths

, , , , (Article



):

struct Article {
    var title: String
    var body: String
    var category: Category
    var isRead: Bool
    ...
    
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , . - , key path Swift , , isRead



:

let articles: [Article] = ...
let readArticles = articles.filter(\.isRead)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , true



- , , , ( ):

let unreadArticles = articles.filter { !$0.isRead }
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , , , : « , key path ? "

. , , key path , true



false



:

prefix func !<T>(keyPath: KeyPath<T, Bool>) -> (T) -> Bool {
    return { !$0[keyPath: keyPath] }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , !



, Bool



key path, , ( ) , , , unreadArticles



:

let unreadArticles = articles.filter(!\.isRead)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , !



, , - .

key paths

  key paths , Equatable



. , , , Equatable



(category



) . , Category



, enum, :

extension Article {
    enum Category {
        case fullLength
        case quickReads
        case basics
        ...
    }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, !



key path , ==



, , , Bool



, API filter



:

func ==<T, V: Equatable>(lhs: KeyPath<T, V>, rhs: V) -> (T) -> Bool {
    return { $0[keyPath: lhs] == rhs }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, key path, :

let fullLengthArticles = articles.filter(\.category == .fullLength)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , , Swift , , . , - , , , - Swift. , , .

, , Swift Sundell, . , , , , .

, « Swift» Twitter .

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