Make a Swift Array conform to Decodable (for JSON parsing)

Array+Decodable.swift

/*
 *
 * An extension for array that takes JSON as a parameter and tries to parse all elements form the given
 * JSON to the Decodable.Type model. Also, in case that the given JSON is not an array type, it will try 
 * to parse single model and append it to the self. 
 *
 * Useful in situations where JSON sometimes can be object and some other times array, e.g. when converting from XML to JSON.
 *
 * This extension uses SwiftyJSON as JSON parsing engine, but it can be made to work with other libraries or manual parsing from Dictionary json.
 */

import SwiftyJSON

public protocol Decodable {
    init?(json: JSON)
}

extension Array: Decodable {
    
    public init?(json: JSON) {
        
        // return early if the json is not valid or Elenent does not confirm to the Decodable protocol
        guard json.exists(), Element.self is Decodable.Type else {
            return nil
        }
        
        if let decodableType = Element.self as? Decodable.Type {
            
            // try to get array from this json
            if let arrayJSON = json.array {
                
                let elements = arrayJSON.flatMap({ decodableType.init(json: $0) as? Element })
                
                self.init()
                self.append(contentsOf: elements)
                
            } else {
                
                // try to get element from json (in case the response contains object instead of the array)
                guard let element = decodableType.init(json: json) as? Element else {
                    return nil
                }
                
                self.init()
                self.append(element)
            }
            
        } else {
            return nil
        }
    }
}


// MARK: Usage
struct User: Decodable {
	
	let name: String
	let surname: String
	
	init?(json: JSON) {
		
		guard let name = json["name"].string, let surname = json["surname"].string else {
			return nil
		}
		
		self.name = name
		self.surname = surname
	}
}

//Let's say you got a JSON array of User objects
let usersJSON: JSON

let users = [User](json: usersJSON)