Swift: Recursive Loop and Flatten Array

Question

I want to better understand recursive looping and flatten in Swift or any other language for that matter.

I have a simple Swift class


class Survey { 
      let items: [SurveyItem]?
}

class SurveyItem { 
      let id: String?
      let items: [SurveyItem]?
}

A Survey has items and each item can have more types of its own.

I want to write a function which assembles all items and subitems in a survey into a single flat array

I would avoid using nullable collections. Just model empty case with an empty collection. — Alexander
– Alexander, Commented May 23, 2019 at 19:24

rob mayoff · Accepted Answer · 2019-05-23 19:16:51Z

7

protocol SurveyItemVending {
    var items: [SurveyItem]? { get }
}

extension Survey: SurveyItemVending { }
extension SurveyItem: SurveyItemVending { }

extension SurveyItemVending {
    var allItemsRecursively: [SurveyItem] {
        let items = self.items ?? []
        return items + items.flatMap { $0.allItemsRecursively }
    }
}

Now you can ask any Survey or SurveyItem for its allItemsRecursively.

answered May 23, 2019 at 19:16

rob mayoff

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