Swift 3: JSON-serializable structs using protocols

Swift3JSONStructs.swift

//: # Swift 3: JSON-serializable structs using protocols
//: Most of the implementation is based on the code in [this blog post](http://codelle.com/blog/2016/5/an-easy-way-to-convert-swift-structs-to-json/)
import Foundation

//: ### Defining the protocols
protocol JSONRepresentable {
    var JSONRepresentation: Any { get }
}

protocol JSONSerializable: JSONRepresentable {}

//: ### Implementing the functionality through protocol extensions
extension JSONSerializable {
    var JSONRepresentation: Any {
        var representation = [String: Any]()

        for case let (label?, value) in Mirror(reflecting: self).children {

            switch value {

            case let value as Dictionary<String, Any>:
                representation[label] = value as AnyObject

            case let value as Array<Any>:
                if let val = value as? [JSONSerializable] {
                    representation[label] = val.map({ $0.JSONRepresentation as AnyObject }) as AnyObject
                } else {
                    representation[label] = value as AnyObject
                }

            case let value:
                representation[label] = value as AnyObject

            default:
                // Ignore any unserializable properties
                break
            }
        }
        return representation as Any
    }
}

extension JSONSerializable {
    func toJSON() -> String? {
        let representation = JSONRepresentation

        guard JSONSerialization.isValidJSONObject(representation) else {
            print("Invalid JSON Representation")
            return nil
        }

        do {
            let data = try JSONSerialization.data(withJSONObject: representation, options: [])

            return String(data: data, encoding: .utf8)
        } catch {
            return nil
        }
    }
}


//: ### Define the Structures
//: Notice how they are conforming to the `JSONSerializable` protocol
struct Author: JSONSerializable {
    var name: String
}

struct Book: JSONSerializable {
    var title: String
    var isbn: String
    var pages: Int

    var authors:[JSONSerializable]
    var extra:[String: Any]
}

//: ### Create a sample object for serialization
let book = Book(
    title: "Mirage",
    isbn: "0399158081",
    pages: 397,
    authors: [
        Author(name: "Clive Cussler"),
        Author(name:"Jack Du Brul")
    ],
    extra: [
        "foo": "bar",
        "baz": 142.226
    ]
)


//: ### Use the protocols to convert the data to JSON
if let json = book.toJSON() {
    print(json)
}