Training a neural network using MPSGraph

At a glance

Project structure

Source bundle/
├── Resources/
│   └── AppDelegate.swift
├── MPSGraphClassifier/
│   ├── ViewController.swift
│   ├── MNISTClassifierGraph.swift
│   ├── Controls.swift
│   ├── Base.lproj/
│   │   └── LaunchScreen.storyboard
│   └── View.xib
├── Common/
│   ├── UIKitSupport.swift
│   ├── MNISTDataSet.swift
│   └── SceneKitSupport.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── MPSGraphClassifier.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 8 project/configuration file(s) and 9 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ViewController"]
    N3["MetalPerformanceShaders / MetalPerformanceShadersGraph APIs"]
    N1 --> N2
    N2 --> N3

Reference code

Resources/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into Metal Performance Shaders Graph.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    ViewController *-- MTLCreateSystemDefaultDevice : gDevice
    ViewController o-- SCNView : sceneKitView
    ViewController o-- UIToolbar : toolbar

Ownership evidence

Resources/AppDelegate.swift:13 — stored dependency or nearest verified ownership anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    var window: UIWindow?
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

Common/UIKitSupport.swift:13 — representative execution boundary

        DispatchQueue.main.async {
            self.text = text
        }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

Common/UIKitSupport.swift:31 — representative type boundary

protocol CanvasDelegate: AnyObject {
    func canvasUpdated()
}

The source explicitly defines local protocol relationships: ViewController → CanvasDelegate.

Access control

Reference code

Resources/AppDelegate.swift:11 — representative boundary

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    var window: UIWindow?
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Controller: ViewController; Delegate: AppDelegate, CanvasDelegate.
• Protocols: CanvasDelegate.
• Methods: application, background, modeSegmentedControlChangeHandler, addCharts, addLabels, viewDidLoad, runButtonTouchHandler, switchDemo.
• Files: Resources/AppDelegate.swift, MPSGraphClassifier/ViewController.swift, Common/MNISTDataSet.swift, MPSGraphClassifier/MNISTClassifierGraph.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, MetalPerformanceShaders, MetalPerformanceShadersGraph, SceneKit through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation