Sample CodemacOSReviewed 2026-07-21View on Apple Developer

Specifying histograms with vImage

At a glance

Item	Summary
Purpose	Calculate the histogram of one image, and apply it to a second image.
App architecture	A Swift sample with the source-visible chain `HistogramSpecificationApp` → `ContentView` → `Accelerate APIs`.
Main patterns	SwiftUI environment injection, Publisher-backed observable state
Project style	3 scanned source file(s) across Swift, organized around ranked entry, type, and file boundaries.

Project structure

Source bundle/
├── HistogramSpecification/
│   ├── HistogramSpecificationApp.swift
│   ├── ContentView.swift
│   ├── HistogramSpecifier.swift
│   └── HistogramSpecification.entitlements
├── Configuration/
│   └── SampleCode.xcconfig
└── HistogramSpecificationSample.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 4 project/configuration file(s) and 4 source declaration(s).

Overall architecture

flowchart LR
    N1["HistogramSpecificationApp"]
    N2["ContentView"]
    N3["Accelerate APIs"]
    N1 --> N2
    N2 --> N3

Reference code

HistogramSpecification/HistogramSpecificationApp.swift:10 — architecture anchor

@main
struct HistogramSpecificationApp: App {
    // ...
}

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
    HistogramSpecificationApp *-- HistogramSpecifier : histogramSpecifier
    ContentView o-- HistogramSpecifier : histogramSpecifier
    Image *-- UUID : id
    Image o-- CGImage : cgImage

Ownership evidence

HistogramSpecification/HistogramSpecificationApp.swift:13 — stored dependency or nearest verified ownership anchor

@main
struct HistogramSpecificationApp: App {
    // ...
    @StateObject private var histogramSpecifier = HistogramSpecifier()
    // ...
}

Owner	Object or state	Relationship	Mutation authority
`HistogramSpecificationApp`	`HistogramSpecifier` (`histogramSpecifier`)	owns wrapper-managed state	Owning lexical scope
`ContentView`	`HistogramSpecifier` (`histogramSpecifier`)	receives environment-provided state	The environment provider is authoritative
`Image`	`UUID` (`id`)	owns value state	Initialized by the owner; the binding is immutable
`Image`	`CGImage` (`cgImage`)	stores or receives	App/module collaborators

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

HistogramSpecification/HistogramSpecificationApp.swift:11 — representative type boundary

struct HistogramSpecificationApp: App {
    // ...
}

Type	Responsibility	Depends on or conforms to
`HistogramSpecificationApp`	Application entry and top-level composition	`App`
`ContentView`	User-interface presentation and input forwarding	`View`
`HistogramSpecifier`	Owns feature behavior and collaborator lifecycle	`ObservableObject`
`Image`	Represents a feature value or composable behavior	`Identifiable`, `Hashable`

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

Access control

Symbol	Access	Verified effect	Likely rationale
`histogramSpecifier` (`HistogramSpecification/HistogramSpecificationApp.swift:13`)	`private`	Use is restricted to the lexical declaration and same-file extensions allowed by Swift.	Inference: keep state mutation or dependency lifetime inside the owning implementation.
`ContentView` (`HistogramSpecification/ContentView.swift:8`)	`implicit internal`	No explicit modifier means the Swift declaration is internal to the module.	Inference: app-target collaboration needs no exported library surface.

Reference code

HistogramSpecification/HistogramSpecificationApp.swift:13 — representative boundary

@main
struct HistogramSpecificationApp: App {
    // ...
    @StateObject private var histogramSpecifier = HistogramSpecifier()
    // ...
}

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

Logic	Owning type or file	Placement rationale
Application entry and top-level composition	`HistogramSpecificationApp`	The source’s `App` suffix makes this role explicit.
User-interface presentation and input forwarding	`ContentView`	The source’s `View` suffix makes this role explicit.

Design patterns

Pattern	Source evidence	Purpose or tradeoff
SwiftUI environment injection	`HistogramSpecification/ContentView.swift:12`	The environment supplies state or a capability without threading it through every initializer.
Publisher-backed observable state	`HistogramSpecification/HistogramSpecifier.swift:35`	Published properties notify observers while mutation remains with the state object.

Naming conventions

Types: App: HistogramSpecificationApp; View: ContentView.
Protocols: no local protocol declaration in the scanned source.
Methods: applyHistogramSpecification, applyHistogramSpecification_PixelBuffer, applyHistogramSpecification_vImageBuffer.
Files: HistogramSpecification/HistogramSpecificationApp.swift, HistogramSpecification/ContentView.swift, HistogramSpecification/HistogramSpecifier.swift.

Architecture takeaways

HistogramSpecificationApp is the main source-visible entry or composition anchor for this sample.
Framework work reaches SwiftUI, Accelerate, Cocoa 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

Source file	Relevant symbols
`HistogramSpecification/HistogramSpecificationApp.swift`	`HistogramSpecificationApp`
`HistogramSpecification/ContentView.swift`	`ContentView`
`HistogramSpecification/HistogramSpecifier.swift`	`HistogramSpecifier`, `Image`

Official Apple documentation