Swift4_JSON_08.swift

import Foundation
import SceneKit

let json = """
{
    "position": [2.0, 5.0, 3.0],
    "rotation": [0.0, 0.73, 0.0, 0.73]
}
""".data(using: .utf8)!

extension SCNVector3: Codable {
    public init(from decoder: Decoder) throws {
        var container = try decoder.unkeyedContainer()
        self.x = try container.decode(CGFloat.self)
        self.y = try container.decode(CGFloat.self)
        self.z = try container.decode(CGFloat.self)
    }
    
    public func encode(to encoder: Encoder) throws {
        var container = encoder.unkeyedContainer()
        try container.encode(self.x)
        try container.encode(self.y)
        try container.encode(self.z)
    }
}

extension SCNVector4: Codable {
    public init(from decoder: Decoder) throws {
        var container = try decoder.unkeyedContainer()
        self.x = try container.decode(CGFloat.self)
        self.y = try container.decode(CGFloat.self)
        self.z = try container.decode(CGFloat.self)
        self.w = try container.decode(CGFloat.self)
    }
    
    public func encode(to encoder: Encoder) throws {
        var container = encoder.unkeyedContainer()
        try container.encode(self.x)
        try container.encode(self.y)
        try container.encode(self.z)
        try container.encode(self.w)
    }
}

struct ModelState: Codable {
    let position: SCNVector3
    let rotation: SCNVector4
}

let decoder = JSONDecoder()
do {
    let state = try decoder.decode(ModelState.self, from: json)
    print(state)
} catch {
    print ("\(error.localizedDescription)")
}

let encoder = JSONEncoder()
let state = ModelState(position: SCNVector3(1, 2, 3), rotation: SCNVector4(0.73, 0, 0, -0.73))
do {
    let data = try encoder.encode(state)
    let text = String(data: data, encoding: .utf8)!
    print(text)
} catch {
    print ("\(error.localizedDescription)")
}