Migrate to Kotlin

[gesellix]

My philosophy behind the Docker client (and as such this repo, too) is to keep the Docker facing side as flexible as possible. Types might be less convenient, so I have no idea whether Kotlin is counter productive. That's what I want to learn and gain some experience.

My main motivation to introduce Kotlin is the library's client facing side of the libraries. A strongly typed api certainly helps to use a library given a capable IDE. That way, the lack of documentation might be compensated to a certain degree.

Things to keep in mind:

• There's no static modifier in Kotlin. static someMethod(){} could be converted to @JvmStatic fun someMethod(), but it would also be valid to simply remove the static modifier and make someMethod() an instance method.
• We should focus on the production code first. Test code can also be converted to Kotlin, but with low priority. I'm a fan of the Groovy Spock framework and there's no equivalent in Kotlin, yet (I didn't find any). Spek seems to be the most similar alternative as of today.

See docker-client/docker-filesocket@620cc55 for a first try at converting from Groovy to Kotlin.

[gesellix]

Hey @shekhargulati, I have no idea how to start exactly with the migration. If you have any specific idea, just tell me! I would start with the low level classes and work from bottom to up. In this actual library the de.gesellix.docker.compose.interpolation should be a good starting point, while de.gesellix.docker.compose.ComposeFileReader could be the final step.

The tests are no real unit tests, they are inspired/copied from the original Docker codebase and as such are quite high level. I guess that helps with the migration and ensures we don't completely break everything, so I would convert the tests only after the production code.

[gesellix]

Finished with d1ba6ee

[gesellix]

Follow-up in the docker-client: gesellix/docker-client#44