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Kotlin/Native libraries

Kotlin compiler specifics

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

$ kotlinc foo.kt -p library -o bar

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

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

$ kotlinc qux.kt -l bar

the above command will produce 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 stdio.def native library definition file provided in your Kotlin/Native distribution

$ cinterop -def  ./samples/csvparser/src/main/c_interop/stdio.def  -o stdio

we obtain stdio.klib.

klib utility

The klib library management utility allows one 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 to specify a repository other than the default one.

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

Several examples

First lets create a library:

$ cinterop -h /usr/include/math.h -pkg libc.math -o math

The library has been created in the current directory:

$ ls math.klib
math.klib

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

$ klib contents math

We can install math to the default repository:

$ klib install math

Remove any traces of it and its build process from the current directory:

$ rm -rf ./math*

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

import libc.math.*
fun main(args: Array<String>) {
    println(sin(2.0))
}

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

$ kotlinc sin.kt -l math -o mysin

And run your program:

$ ./mysin.kexe
0.9092974268256817

Have fun!

Advanced topics

Library search sequence

When given -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

WARNING: the library format is very preliminary. It is subject to change right under your fingers. And it can incompatibly change from release to release until Kotlin/Native is stabilized.

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

foo.klib when unpacked as foo/ gives us:

  • foo/

    • 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 exemplar layout can be found in klib/stdlib directory of your installation.