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feat: Add C++ to Swift to Android integration example (#24)
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‎.gitignore‎

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*.iml
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.gradle
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**/.gradle/
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/local.properties
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/.idea
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.DS_Store
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/build
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build/
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/captures
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.externalNativeBuild
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.cxx
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**/.cxx/
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local.properties
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jniLibs
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# C++ build artifacts
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**/prebuilt/
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# Swift build artifacts
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**/.build/
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**/Package.resolved

‎README.md‎

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

‎hello-cpp-swift/README.md‎

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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#ifndef CALCULATOR_H
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#define CALCULATOR_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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int add(int a, int b);
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int multiply(int a, int b);
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#ifdef __cplusplus
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}
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#endif
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#endif

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