feat: Add C++ to Swift to Android integration example

.gitignore

@@ -1,11 +1,18 @@
 *.iml
-.gradle
+**/.gradle/
 /local.properties
 /.idea
 .DS_Store
-/build
+build/
 /captures
 .externalNativeBuild
-.cxx
+**/.cxx/
 local.properties
 jniLibs
+
+# C++ build artifacts
+**/prebuilt/
+
+# Swift build artifacts
+**/.build/
+**/Package.resolved

README.md

@@ -29,6 +29,16 @@ This approach is ideal for production Android applications where you want to wri
 business logic, algorithms, or libraries in Swift, while maintaining a standard
 Kotlin/Java frontend.
 
+## C++ Integration Example
+
+The **[hello-cpp-swift](hello-cpp-swift/)** example demonstrates how to integrate
+C++ libraries into Android applications through Swift. This example packages a C++
+library as an artifactbundle, imports it as a Swift binary target, and exposes it
+to Android using swift-java for automatic JNI generation.
+
+This pattern is useful when you have existing C++ code and want to leverage Swift's
+type safety and swift-java's automatic bridging to create Android-compatible libraries.
+
 ## Other Examples
 
 For those who want to explore alternative integration patterns or understand

hello-cpp-swift/README.md

@@ -0,0 +1,89 @@
+# C++ to Swift to Android Integration
+
+This example demonstrates how to call C++ code from Android through Swift. The app uses a C++ library that provides basic calculator functions (add and multiply), wraps them in Swift, and calls them from an Android Kotlin app.
+
+## Overview
+
+The project is structured into three main parts:
+
+1. **`cpp-lib`**: A C++ library with basic calculator functions (`add` and `multiply`). This is built using CMake and packaged as an artifactbundle for consumption by Swift.
+
+2. **`swift-lib`**: A Swift package that wraps the C++ functions and exposes them to Android using [swift-java](https://github.com/swiftlang/swift-java). The Swift code calls the C++ functions and provides JNI bindings automatically.
+
+3. **`app`**: A standard Android application written in Kotlin that calls the Swift-wrapped C++ functions and displays the results.
+
+## Prerequisites
+
+Before you can build and run this project, you need to have the following installed:
+
+* **Basic setup**: Follow the Prerequisites and Setup instructions in [hello-swift-java/README.md](../hello-swift-java/README.md) to install JDK, Swiftly, Swift SDK for Android, and publish the swift-java packages locally.
+* **Android NDK**: Required to build the C++ library. Set the `ANDROID_NDK_HOME` environment variable to your NDK installation path.
+
+## Setup and Configuration
+
+### 1. Build the C++ Library
+
+Before building the Android app, you need to build the C++ library:
+
+```bash
+cd hello-cpp-swift/cpp-lib
+./build-android-static.sh
+```
+
+This will create the `prebuilt/HelloWorldCpp.artifactbundle` directory containing the compiled C++ static libraries for all Android architectures (arm64-v8a, armeabi-v7a, x86_64).
+
+## Running the example
+
+1. Open the `swift-android-examples` project in Android Studio.
+
+2. Select the `hello-cpp-swift:app` Gradle target.
+
+3. Run the app on an Android emulator or a physical device.
+
+4. The app will display the results of C++ calculations (10 + 5 and 10 × 5) called through Swift.
+
+## Building from command line
+
+```bash
+# From the project root directory
+./gradlew :hello-cpp-swift:app:assembleDebug
+
+# Install on device/emulator
+./gradlew :hello-cpp-swift:app:installDebug
+```
+
+## How it works
+
+1. **C++ Layer** (`cpp-lib/src/calculator.cpp`):
+   ```cpp
+   int add(int a, int b) {
+       return a + b;
+   }
+   ```
+
+2. **Swift Layer** (`swift-lib/Sources/HelloCppSwift/Calculator.swift`):
+   ```swift
+   import HelloWorldCpp
+
+   public func addNumbers(_ a: Int32, _ b: Int32) -> Int32 {
+       return add(a, b)
+   }
+   ```
+
+3. **Android/Kotlin Layer** (`app/MainActivity.kt`):
+   ```kotlin
+   val sum = com.example.hellocppswift.HelloCppSwift.addNumbers(10, 5)
+   ```
+
+The Swift code is automatically wrapped with JNI bindings using the `swift-java` JExtract plugin, making it callable from Kotlin/Java code.
+
+## Rebuilding the C++ Library
+
+If you make changes to the C++ code, you need to rebuild the artifactbundle:
+
+```bash
+cd hello-cpp-swift/cpp-lib
+./build-android-static.sh
+```
+
+Then rebuild the Android app to pick up the changes.

hello-cpp-swift/app/build.gradle.kts

@@ -0,0 +1,47 @@
+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.kotlin.android)
+}
+
+android {
+    namespace = "com.example.hellocppswift"
+    compileSdk = 36
+
+    defaultConfig {
+        applicationId = "com.example.hellocppswift"
+        minSdk = 28
+        targetSdk = 36
+        versionCode = 1
+        versionName = "1.0"
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_11
+        targetCompatibility = JavaVersion.VERSION_11
+    }
+}
+
+kotlin {
+    compilerOptions {
+        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_11)
+    }
+}
+
+dependencies {
+    implementation(libs.androidx.core.ktx)
+    implementation(libs.androidx.appcompat)
+    implementation(libs.material)
+    implementation(libs.androidx.constraintlayout)
+    implementation("org.swift.swiftkit:swiftkit-core:1.0-SNAPSHOT")
+    implementation(project(":hello-cpp-swift:swift-lib"))
+}

hello-cpp-swift/app/src/main/AndroidManifest.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <application
+        android:allowBackup="true"
+        android:label="@string/app_name"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.AppCompat.Light.DarkActionBar">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
+
+</manifest>

hello-cpp-swift/app/src/main/java/com/example/hellocppswift/MainActivity.kt

@@ -0,0 +1,32 @@
+package com.example.hellocppswift
+
+import android.os.Bundle
+import android.view.Gravity
+import android.widget.FrameLayout
+import android.widget.TextView
+import androidx.appcompat.app.AppCompatActivity
+
+class MainActivity : AppCompatActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+
+        val textView = TextView(this).apply {
+            textSize = 24f
+            textAlignment = TextView.TEXT_ALIGNMENT_CENTER
+            setPadding(32, 32, 32, 32)
+            gravity = Gravity.CENTER
+        }
+
+        val sum = com.example.hellocppswift.HelloCppSwift.addNumbers(10, 5)
+        val product = com.example.hellocppswift.HelloCppSwift.multiplyNumbers(10, 5)
+
+        textView.text = "C++ via Swift Calculations:\n\n10 + 5 = $sum\n10 × 5 = $product"
+
+        val container = FrameLayout(this).apply {
+            setPadding(0, 200, 0, 0)
+            addView(textView)
+        }
+
+        setContentView(container)
+    }
+}

hello-cpp-swift/app/src/main/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">Hello C++ Swift</string>
+</resources>

hello-cpp-swift/cpp-lib/CMakeLists.txt

@@ -0,0 +1,21 @@
+cmake_minimum_required(VERSION 3.18)
+project(HelloWorldCpp VERSION 1.0.0 LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+set(SOURCES
+    src/calculator.cpp
+)
+
+set(HEADERS
+    include/calculator.h
+)
+
+add_library(${PROJECT_NAME} STATIC ${SOURCES} ${HEADERS})
+
+target_include_directories(${PROJECT_NAME}
+    PUBLIC
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+        $<INSTALL_INTERFACE:include>
+)

hello-cpp-swift/cpp-lib/build-android-static.sh

@@ -0,0 +1,115 @@
+#!/bin/bash
+
+set -e
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+cd "$SCRIPT_DIR"
+
+if [ -z "$ANDROID_NDK_HOME" ]; then
+    echo "Error: ANDROID_NDK_HOME environment variable is not set"
+    echo "Please set it to your Android NDK installation path"
+    exit 1
+fi
+
+if [ ! -d "$ANDROID_NDK_HOME" ]; then
+    echo "Error: ANDROID_NDK_HOME points to non-existent directory: $ANDROID_NDK_HOME"
+    exit 1
+fi
+
+ANDROID_TOOLCHAIN="$ANDROID_NDK_HOME/build/cmake/android.toolchain.cmake"
+
+if [ ! -f "$ANDROID_TOOLCHAIN" ]; then
+    echo "Error: Android toolchain file not found at: $ANDROID_TOOLCHAIN"
+    exit 1
+fi
+
+ANDROID_API=28
+
+ABIS=(
+    "arm64-v8a:android-aarch64"
+    "armeabi-v7a:android-armv7"
+    "x86_64:android-x86_64"
+)
+
+echo "Building HelloWorldCpp static libraries for Android..."
+
+for ABI_ENTRY in "${ABIS[@]}"; do
+    ABI="${ABI_ENTRY%%:*}"
+    echo "Building for $ABI..."
+
+    BUILD_DIR="build/android-static/$ABI"
+    mkdir -p "$BUILD_DIR"
+
+    cmake -S . -B "$BUILD_DIR" \
+        -DCMAKE_TOOLCHAIN_FILE="$ANDROID_TOOLCHAIN" \
+        -DANDROID_ABI="$ABI" \
+        -DANDROID_PLATFORM="android-$ANDROID_API" \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_CXX_STANDARD=17
+
+    cmake --build "$BUILD_DIR" --config Release
+
+    echo "✓ Built $ABI"
+done
+
+echo ""
+echo "Creating artifactbundle..."
+
+ARTIFACTBUNDLE_DIR="prebuilt/HelloWorldCpp.artifactbundle"
+
+for ABI_ENTRY in "${ABIS[@]}"; do
+    ABI="${ABI_ENTRY%%:*}"
+    BUNDLE_DIR="${ABI_ENTRY##*:}"
+
+    mkdir -p "$ARTIFACTBUNDLE_DIR/$BUNDLE_DIR/Headers"
+
+    cp "build/android-static/$ABI/libHelloWorldCpp.a" "$ARTIFACTBUNDLE_DIR/$BUNDLE_DIR/"
+
+    cp include/calculator.h "$ARTIFACTBUNDLE_DIR/$BUNDLE_DIR/Headers/"
+    cp include/module.modulemap "$ARTIFACTBUNDLE_DIR/$BUNDLE_DIR/Headers/"
+
+    echo "✓ Created artifactbundle for $BUNDLE_DIR"
+done
+
+cat > "$ARTIFACTBUNDLE_DIR/info.json" << 'EOF'
+{
+  "schemaVersion": "1.0",
+  "artifacts": {
+    "HelloWorldCpp": {
+      "version": "1.0.0",
+      "type": "staticLibrary",
+      "variants": [
+        {
+          "path": "android-aarch64/libHelloWorldCpp.a",
+          "supportedTriples": ["aarch64-unknown-linux-android"],
+          "staticLibraryMetadata": {
+            "headerPaths": ["android-aarch64/Headers"],
+            "moduleMapPath": "android-aarch64/Headers/module.modulemap"
+          }
+        },
+        {
+          "path": "android-armv7/libHelloWorldCpp.a",
+          "supportedTriples": ["armv7-unknown-linux-android"],
+          "staticLibraryMetadata": {
+            "headerPaths": ["android-armv7/Headers"],
+            "moduleMapPath": "android-armv7/Headers/module.modulemap"
+          }
+        },
+        {
+          "path": "android-x86_64/libHelloWorldCpp.a",
+          "supportedTriples": ["x86_64-unknown-linux-android"],
+          "staticLibraryMetadata": {
+            "headerPaths": ["android-x86_64/Headers"],
+            "moduleMapPath": "android-x86_64/Headers/module.modulemap"
+          }
+        }
+      ]
+    }
+  }
+}
+EOF
+
+echo "✓ Generated info.json"
+echo ""
+echo "All Android static libraries built successfully!"
+echo "Artifactbundle created at: $ARTIFACTBUNDLE_DIR"

hello-cpp-swift/cpp-lib/include/calculator.h

@@ -0,0 +1,15 @@
+#ifndef CALCULATOR_H
+#define CALCULATOR_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int add(int a, int b);
+int multiply(int a, int b);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

hello-cpp-swift/cpp-lib/include/module.modulemap

@@ -0,0 +1,4 @@
+module HelloWorldCpp {
+    header "calculator.h"
+    export *
+}