FAQ.md

Q: How do I run my program?

A: Define a top level function fun main(args: Array<String>) or just fun main() if you are not interested in passed arguments, please ensure it's not in a package. Also compiler switch -entry could be used to make any function taking Array<String> or no arguments and return Unit as an entry point.

Q: What is Kotlin/Native memory management model?

A: Kotlin/Native provides an automated memory management scheme, similar to what Java or Swift provides. The current implementation includes an automated reference counter with a cycle collector to collect cyclical garbage.

Q: How do I create a shared library?

A: Use the -produce dynamic compiler switch, or binaries.sharedLib() in Gradle, i.e.

targets {
    fromPreset(presets.iosArm64, 'mylib') {
        binaries.sharedLib()
    }
}

It will produce a platform-specific shared object (.so on Linux, .dylib on macOS, and .dll on Windows targets) and a C language header, allowing the use of all public APIs available in your Kotlin/Native program from C/C++ code. See samples/python_extension for an example of using such a shared object to provide a bridge between Python and Kotlin/Native.

Q: How do I create a static library or an object file?

A: Use the -produce static compiler switch, or binaries.staticLib() in Gradle, i.e.

targets {
    fromPreset(presets.iosArm64, 'mylib') {
        binaries.staticLib()
    }
}

It will produce a platform-specific static object (.a library format) and a C language header, allowing you to use all the public APIs available in your Kotlin/Native program from C/C++ code.

Q: How do I run Kotlin/Native behind a corporate proxy?

A: As Kotlin/Native needs to download a platform specific toolchain, you need to specify -Dhttp.proxyHost=xxx -Dhttp.proxyPort=xxx as the compiler's or gradlew arguments, or set it via the JAVA_OPTS environment variable.

Q: How do I specify a custom Objective-C prefix/name for my Kotlin framework?

A: Use the -module-name compiler option or matching Gradle DSL statement, i.e.

targets {
    fromPreset(presets.iosArm64, 'myapp') {
        binaries.framework()
        compilations.main.extraOpts '-module-name', 'TheName'
    }
}

Q: How do I rename the iOS framework? (default name is <project name>.framework)

A: Use the baseName option. This will also set the module name.

targets {
    fromPreset(presets.iosArm64, 'myapp') {
       binaries {
          framework {
              baseName = "TheName"
          }
       }
    }
}

Q: How do I enable bitcode for my Kotlin framework?

A: By default gradle plugin adds it on iOS target.

• For debug build it embeds placeholder LLVM IR data as a marker.
• For release build it embeds bitcode as data.

Or commandline arguments: -Xembed-bitcode (for release) and -Xembed-bitcode-marker (debug)

Setting this in a Gradle DSL:

targets {
    fromPreset(presets.iosArm64, 'myapp') {
        binaries {
            framework {
                // Use "marker" to embed the bitcode marker (for debug builds).
                // Use "disable" to disable embedding.
                embedBitcode "bitcode" // for release binaries.
            }
        }
    }
}

These options have nearly the same effect as clang's -fembed-bitcode/-fembed-bitcode-marker and swiftc's -embed-bitcode/-embed-bitcode-marker.

Q: Why do I see InvalidMutabilityException?

A: It likely happens, because you are trying to mutate a frozen object. An object can transfer to the frozen state either explicitly, as objects reachable from objects on which the kotlin.native.concurrent.freeze is called, or implicitly (i.e. reachable from enum or global singleton object - see the next question).

Q: How do I make a singleton object mutable?

A: Currently, singleton objects are immutable (i.e. frozen after creation), and it's generally considered good practise to have the global state immutable. If for some reason you need a mutable state inside such an object, use the @konan.ThreadLocal annotation on the object. Also the kotlin.native.concurrent.AtomicReference class could be used to store different pointers to frozen objects in a frozen object and automatically update them.

Q: How can I compile my project against the Kotlin/Native master?

A: One of the following should be done:

For the CLI, you can compile using gradle as stated in the README (and if you get errors, you can try to do a ./gradlew clean):

./gradlew dependencies:update
./gradlew dist distPlatformLibs

You can then set the KONAN_HOME env variable to the generated dist folder in the git repository.

For Gradle, you can use Gradle composite builds like this:

# Set with the path of your kotlin-native clone
export KONAN_REPO=$PWD/../kotlin-native

# Run this once since it is costly, you can remove the `clean` task if not big changes were made from the last time you did this
pushd $KONAN_REPO && git pull && ./gradlew clean dependencies:update dist distPlatformLibs && popd

# In your project, you set have to the org.jetbrains.kotlin.native.home property, and include as composite the shared and gradle-plugin builds
./gradlew check -Porg.jetbrains.kotlin.native.home=$KONAN_REPO/dist --include-build $KONAN_REPO/shared --include-build $KONAN_REPO/tools/kotlin-native-gradle-plugin