How to encode MKPolyline

encodable_polyline.swift

import MapKit
extension MKPolyline: Encodable {
    public func encode(to encoder: Encoder) throws {
        var container = encoder.unkeyedContainer()
        for idx in 0..<self.pointCount {
            let p = self.points()[idx]
            try container.encode(p.x)
            try container.encode(p.y)
        }
    }
}

let pts = UnsafeMutablePointer<MKMapPoint>.allocate(capacity: 3)
pts[0] = MKMapPoint(x: 0.5, y: 0.5)
pts[1] = MKMapPoint(x: 0.2, y: 0.2)
pts[2] = MKMapPoint(x: 1.0, y: 1.0)

let polyline = MKPolyline(points: pts, count: 3)

String(data: JSONEncoder().encode(polyline), encoding: .utf8)
// $R3: String? = "[0.5,0.5,0.20000000000000001,0.20000000000000001,1,1]"