CodablePerformance.swift

import Foundation

public struct Airport: Codable {
    let name: String
    let iata: String
    let icao: String
    let coordinates: [Double]

    public struct Runway: Codable {
        enum Surface: String, Codable {
            case rigid, flexible, gravel, sealed, unpaved, other
        }

        let direction: String
        let distance: Int
        let surface: Surface
    }

    let runways: [Runway]
}

extension Airport {
    public init(json: [String: Any]) {
        guard let name = json["name"] as? String,
            let iata = json["iata"] as? String,
            let icao = json["icao"] as? String,
            let coordinates = json["coordinates"] as? [Double],
            let runways = json["runways"] as? [[String: Any]]
        else {
            fatalError("Cannot initialize Airport from JSON")
        }

        self.name = name
        self.iata = iata
        self.icao = icao
        self.coordinates = coordinates
        self.runways = runways.map { Runway(json: $0) }
    }
}

extension Airport.Runway {
    public init(json: [String: Any]) {
        guard let direction = json["direction"] as? String,
            let distance = json["distance"] as? Int,
            let surfaceRawValue = json["surface"] as? String,
            let surface = Surface(rawValue: surfaceRawValue)
            else {
                fatalError("Cannot initialize Runway from JSON")
        }

        self.direction = direction
        self.distance = distance
        self.surface = surface
    }
}

let data = try! Data(contentsOf: URL(fileURLWithPath: ProcessInfo.processInfo.arguments[1]))

func measure(_ block: () -> ()) {
    let start = Date()
    for _ in 0..<10 {
        block()
    }
    let end = Date()
    print("elapsed:", end.timeIntervalSince(start))
}

measure {
    let decoder = JSONDecoder()
    let airports = try! decoder.decode([Airport].self, from: data)
    assert(airports.count == 10000)
}

measure {
    let json = try! JSONSerialization.jsonObject(with: data, options: []) as! [[String: Any]]
    let airports = json.map{ Airport(json: $0) }
    assert(airports.count == 10000)
}

Dockerfile

FROM swift:5.3-focal as build

COPY ./ ./
RUN swift build -c release

CMD ["./.build/release/CodablePerformance", "./airports10000.json"]

airports10000.json は ここ から拾ってきた

雑な計測結果
Codable on mac: 2.3s
JSONS.. on mac: 1.0s
Codable on docker4mac: 9.2s
JSONS.. on docker4mac: 2.3s

全体的な実装はこちらのリポジトリから拝借しました https://github.com/Flight-School/CodablePerformance