SwiftUI with SwiftDSL vs SwiftUI not SwiftDSL

swiftui.swift

import UIKit
import SwiftUI

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
    var window: UIWindow?
    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            self.window = window
        }
        window?.rootViewController = UIHostingController(rootView: EmptyView())
        window?.makeKeyAndVisible()
        sleep(1)

        print("---------- start -------------")
        let date1 = Date()
        window?.rootViewController = UIHostingController(rootView: SwiftDSLView())
        window?.makeKeyAndVisible()
        print("SwiftDSLView: \(Date().timeIntervalSince(date1))")
        sleep(1)


        let date2 = Date()
        window?.rootViewController = UIHostingController(rootView: SwiftNoDSLView())
        window?.makeKeyAndVisible()
        print("SwiftNoDSLView: \(Date().timeIntervalSince(date2))")

        window?.rootViewController = UIHostingController(rootView: EmptyView())
        window?.makeKeyAndVisible()
        print("---------- end -------------")
    }
}


import SwiftUI

class ViewModel: ObservableObject {
    @Published var counter = 0
    
    func start() {
        for i in (1...100000) {
            counter = i
        }
    }
}

struct SwiftDSLView: View {
    @ObservedObject(initialValue: ViewModel()) var viewModel
    var counter: Int { viewModel.counter }
    var body: some View {
        Group {
            if counter % 2 == 0 {
                Text("\(self.counter)")
            } else {
                Text("\(self.counter)")
            }
        }
        .onAppear {
            self.viewModel.start()
        }
    }
}

struct SwiftNoDSLView: View {
    @ObservedObject(initialValue: ViewModel()) var viewModel
    var counter: Int { viewModel.counter }
    var body: some View {
        return Group { () -> Text in
            switch counter % 2 == 0 {
            case true:
                return Text("\(counter)")
            case false:
                return Text("\(counter)")
            }
        }
        .onAppear {
            self.viewModel.start()
        }
    }
}

誤差

---------- start -------------
SwiftDSLView: 0.005283951759338379
SwiftNoDSLView: 0.004162907600402832
---------- end -------------

ここらへんから

https://twitter.com/noppefoxwolf/status/1179458826942046208?s=20