Training a neural network to recognize digits

At a glance

Project structure

Source bundle/
├── BNNS-Training-Sample/
│   ├── main.swift
│   ├── Digits.swift
│   ├── TrainingSample.swift
│   ├── Evaluation.swift
│   ├── FullyConnected.swift
│   ├── FusedConvBatchNorm.swift
│   ├── InputAndLabelGeneration.swift
│   ├── Loss.swift
│   ├── Pooling.swift
│   └── ResourceDeallocation.swift
└── BNNS-Training-Sample.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 3 project/configuration file(s) and 2 source declaration(s).

Overall architecture

flowchart LR
    N1["Digits"]
    N2["Accelerate APIs"]
    N1 --> N2

Reference code

BNNS-Training-Sample/Digits.swift:14 — architecture anchor

    struct Digits {
        // ...
    }

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 Accelerate.

Ownership and state

classDiagram
    Digits *-- Array : zero
    Digits *-- Array : one
    Digits *-- Array : two
    Digits *-- Array : three

Ownership evidence

BNNS-Training-Sample/Digits.swift:18 — stored dependency or nearest verified ownership anchor

        static let zero: [Float] = [0, 0, 1, 1, 0, 0,
                                    0, 1, 0, 0, 1, 0,
                                    0, 1, 0, 0, 1, 0,
                                    0, 1, 0, 0, 1, 0,
                                    0, 1, 0, 0, 1, 0,
                                    0, 0, 1, 1, 0, 0]

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.

Class and protocol design

BNNS-Training-Sample/Digits.swift:14 — representative type boundary

    struct Digits {
        // ...
    }

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

BNNS-Training-Sample/Digits.swift:14 — representative boundary

    struct Digits {
        // ...
    }

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: feature-specific names rather than reusable layer suffixes.
• Protocols: no local protocol declaration in the scanned source.
• Methods: testExample, runTrainingExample, forwardPass, backwardPass, optimizerStep, test, backwardFully, backwardFused.
• Files: BNNS-Training-Sample/Digits.swift, BNNS-Training-Sample/TrainingSample.swift.

Architecture takeaways

• Digits is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Accelerate 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation