Simple JSON task using new Decodable protocol

Decodable.swift

// Copyright 2017 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import Foundation

var baseTs: UInt64 = 0
func ts(_ label: String) {
    let ts = mach_absolute_time()
    print(label + String(format: ": %.3f", Double(ts - baseTs) * 1e-6))
}

let data = try Data(contentsOf: URL(fileURLWithPath: "/tmp/update.json"))

struct Req: Decodable {
    var method: String
    var params: Params
}

struct Params: Decodable {
    var viewId: String
    var update: Update
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.viewId = try container.decode(String.self, forKey: .viewId)
        self.update = try container.decode(Update.self, forKey: .update)
    }
    enum CodingKeys: String, CodingKey {
        case viewId = "view_id"
        case update
    }
}

struct Update: Decodable {
    var ops: [Op]
    var pristine: Bool
}

struct Op: Decodable {
    var op: String
    var n: Int
    var lines: [Line]?
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.op = try container.decode(String.self, forKey: .op)
        self.n = try container.decode(Int.self, forKey: .n)
        self.lines = try container.decodeIfPresent(Array<Line>.self, forKey: .lines)
    }
    enum CodingKeys: String, CodingKey {
        case op
        case n
        case lines
    }
}

struct Line: Decodable {
    var text: String
    var styles: [Int]
}

func benchNewJson() throws {
    baseTs = mach_absolute_time()
    let jsonDecoder = JSONDecoder()
    ts("created decoder")
    let obj = try jsonDecoder.decode(Req.self, from: data)
    ts("decoded")
    var total = 0
    var textLen = 0
    for op in obj.params.update.ops {
        total += op.n
        if let lines = op.lines {
            for line in lines {
                textLen += line.text.count
            }
        }
    }
    ts("after traversal")
    print("Decodable result:", total, textLen)
}

try benchNewJson()