Calling APIs Across Language Boundaries

At a glance

Project structure

Source bundle/
├── Swift-and-Cplusplus-InteroperabilityShowcase/
│   ├── SwiftCppInteroperabilityShowcaseApp.swift
│   ├── ContentView.swift
│   └── EnchantedForest.swift
├── ForestUI/
│   ├── ForestView.swift
│   └── Tree+UI.swift
├── ForestBuilder/
│   ├── ForestBuilder.h
│   ├── MagicForestBuilder.mm
│   └── MagicForest.swift
├── Forest/
│   ├── Forest.cpp
│   ├── Forest.h
│   └── Tree.cpp
└── ForestTestSupport/
    └── Tree+Equatable.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C++, C/Objective-C header, Objective-C++, Swift.
• The verified tree contains 4 project/configuration file(s) and 6 source declaration(s).

Overall architecture

flowchart LR
    N1["SwiftCppInteroperabilityShowcaseApp"]
    N2["ContentView"]
    N3["SwiftUI APIs"]
    N1 --> N2
    N2 --> N3

Reference code

Swift-and-Cplusplus-InteroperabilityShowcase/SwiftCppInteroperabilityShowcaseApp.swift:10 — architecture anchor

@main
struct SwiftCppInteroperabilityShowcaseApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

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 Swift.

Ownership and state

classDiagram
    ForestView o-- Forest : forest
    CustomOneTreeForest *-- String : name
    CustomOneTreeForest *-- Int : numTrees
    CustomOneTreeForest o-- TreeKind : kind

Ownership evidence

ForestUI/ForestView.swift:12 — stored dependency or nearest verified ownership anchor

public struct ForestView: View {
    let forest: Forest
    // ...
}

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.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@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.

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

Swift-and-Cplusplus-InteroperabilityShowcase/SwiftCppInteroperabilityShowcaseApp.swift:11 — representative type boundary

@main
struct SwiftCppInteroperabilityShowcaseApp: App {
    // ...
            ContentView()
    // ...
}

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

Access control

Reference code

ForestBuilder/MagicForest.swift:15 — representative boundary

    public init(oakForestName name: String, numTrees: Int) {
        self.name = name
        self.numTrees = numTrees
        kind = TreeKind.Oak
    }

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: App: SwiftCppInteroperabilityShowcaseApp; View: ContentView, ForestView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: createForest.
• Files: Swift-and-Cplusplus-InteroperabilityShowcase/SwiftCppInteroperabilityShowcaseApp.swift, Swift-and-Cplusplus-InteroperabilityShowcase/ContentView.swift, ForestUI/ForestView.swift, ForestBuilder/MagicForest.swift.

Architecture takeaways

• SwiftCppInteroperabilityShowcaseApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Forest, ForestBuilder, SwiftUI, ForestTestSupport 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