JSON Serialization driven by Swift Reflection

about.md

A swift playground experiment in making a Swift struct to JSON serialization.

The approach currently fails for arrays, but those can be handled much like dictionaries and optionals.

json_serialization.swift

//: Playground - noun: a place where people can play

struct PhoneNumber {
    let countryCode :Int
    let number :Int
}

struct Person {
    let name :String
    let phoneNumber :[String : PhoneNumber]
}

let jane = Person(name: "Jane Doe", phoneNumber: ["cell": PhoneNumber(countryCode: 1, number: 5555555)])

let jM = Mirror(reflecting: jane)

let pC = jM.children

for case let (label, value) in pC {
    label
    value
}

protocol JSON {
    func asJSON() -> Any?
}

extension JSON {
    func asJSON() -> Any? {
        let mirror = Mirror(reflecting: self)
        if mirror.children.count == 0 {
            return self
        }
        var out: [String:Any] = [:]
        for case let (key?, value) in mirror.children {
            if let value = value as? JSON {
                out[key] = value.asJSON()
            }
        }
        return out
    }
}

extension String :JSON {}
extension Int :JSON {}
extension Float :JSON {}
extension Bool :JSON {}
extension Optional :JSON {
    func asJSON() -> Any? {
        if let value = self as? JSON {
            return value.asJSON
        } else {
            return nil
        }
    }
}
extension Dictionary :JSON {
    func asJSON() -> Any? {
        var out :[String: Any] = [:]
        if Key.self == String.self {
            for (key, value) in self {
                out[key as! String] = value
            }
        }
        return out
    }
}

"hi".asJSON()
3.asJSON()
true.asJSON()

extension Person :JSON {}
extension PhoneNumber :JSON {}

let janeJSON = jane.asJSON()

(janeJSON as! [String:Any])["phoneNumber"]
    
["hi":5].asJSON()