The Swift Reflection API and what you can do with it


released Fri, 01 Mar 2019
Swift Version 5.0


Swift's reflection capabilities are based around a struct called Mirror. You create a mirror for a particular subject and the mirror will then let you query it.

Before we look at the API, let's define a simple data structure that we can experiment on.

import Foundation

public class Store {

     let storesToDisk: Bool = true


public class BookmarkStore: Store {

     let itemCount: Int = 10


public struct Bookmark {

    enum Group {

       case tech

       case news


    private let store = {

        return BookmarkStore()


    let title: String?

    let url: URL

    let keywords: [String]

    let group: Group


let aBookmark = Bookmark(title: \"Appventure\", url: URL(string: \"\")!, keywords: [\"Swift\", \"iOS\", \"OSX\"], group: .tech)

So, we have a Bookmark. Bookmarks can have titles, urls, keywords, and bookmarks can belong to a Group. There is also a BookmarkStore and a more general Store. So, how do we query this data structure at runtime?