Kotlin/Native libraries

Kotlin compiler specifics

To produce a library with the Kotlin/Native compiler use the -produce library or -p library flag. For example:

$ kotlinc foo.kt -p library -o bar

the above command will produce a bar.klib with the compiled contents of foo.kt.

To link to a library use the -library <name> or -l <name> flag. For example:

$ kotlinc qux.kt -l bar

the above command will produce a program.kexe out of qux.kt and bar.klib

cinterop tool specifics

The cinterop tool produces .klib wrappers for native libraries as its main output. For example, using the simple libgit2.def native library definition file provided in your Kotlin/Native distribution

$ cinterop -def samples/gitchurn/src/nativeInterop/cinterop/libgit2.def -compiler-option -I/usr/local/include -o libgit2

we will obtain libgit2.klib.

See more details in INTEROP.md

klib utility

The klib library management utility allows you to inspect and install the libraries.

The following commands are available.

To list library contents:

$ klib contents <name>

To inspect the bookkeeping details of the library

$ klib info <name>

To install the library to the default location use

$ klib install <name>

To remove the library from the default repository use

$ klib remove <name>

All of the above commands accept an additional -repository <directory> argument for specifying a repository different to the default one.

$ klib <command> <name> -repository <directory>

Several examples

First let's create a library. Place the tiny library source code into kotlinizer.kt:

package kotlinizer
val String.kotlinized
    get() = "Kotlin $this"

$ kotlinc kotlinizer.kt -p library -o kotlinizer

The library has been created in the current directory:

$ ls kotlinizer.klib
kotlinizer.klib

Now let's check out the contents of the library:

$ klib contents kotlinizer

We can install kotlinizer to the default repository:

$ klib install kotlinizer

Remove any traces of it from the current directory:

$ rm kotlinizer.klib

Create a very short program and place it into a use.kt :

import kotlinizer.*

fun main(args: Array<String>) {
    println("Hello, ${"world".kotlinized}!")
}

Now compile the program linking with the library we have just created:

$ kotlinc use.kt -l kotlinizer -o kohello

And run the program:

$ ./kohello.kexe
Hello, Kotlin world!

Have fun!

Advanced topics

Library search sequence

When given a -library foo flag, the compiler searches the foo library in the following order:

* Current compilation directory or an absolute path.

* All repositories specified with `-repo` flag.

* Libraries installed in the default repository (For now the default is  `~/.konan`, however it could be changed by setting **KONAN_DATA_DIR** environment variable).

* Libraries installed in `$installation/klib` directory.

The library format

Kotlin/Native libraries are zip files containing a predefined directory structure, with the following layout:

foo.klib when unpacked as foo/ gives us:

  - foo/
    - $component_name/
      - ir/
        - Seriaized Kotlin IR.
      - targets/
        - $platform/
          - kotlin/
            - Kotlin compiled to LLVM bitcode.
          - native/
            - Bitcode files of additional native objects.
        - $another_platform/
          - There can be several platform specific kotlin and native pairs.
      - linkdata/
        - A set of ProtoBuf files with serialized linkage metadata.
      - resources/
        - General resources such as images. (Not used yet).
      - manifest - A file in *java property* format describing the library.

An example layout can be found in klib/stdlib directory of your installation.