Add Kotlin extension functions

[Miha Krajnc]

This is a suggestion, it would be handy to have Kotlin extension functions for all Converters.register* functions.

For example, Converters.registerDateTime(GsonBuilder) would become:

fun GsonBuilder.registerDateTime(): GsonBuilder {
    registerTypeAdapter(DATE_TIME_TYPE, DateTimeConverter())
    return this
}

And consequentially, Converters.registerDateTime(new GsonBuilder()).create(); would become:

GsonBuilder().registerDateTime().create()

[Greg]

@mihakrajnc great idea!

Are you able to create a PR that adds Kotlin compilation and these extension functions?

[Miha Krajnc]

@gkopff Sure thing, I'll try to put it together by the end of the week.

Do you do anything special to compile it now? mvn compile / mvn package? It's been a while since I did Maven :)

[Greg]

It gets published to Maven central via mvn release:prepare mvn release:perform, which I assume must do a mvn package to build the artefacts to upload.

I've used this previously to compile Kotlin:

  <build>
    <sourceDirectory>src/main/kotlin</sourceDirectory>
    <testSourceDirectory>src/test/kotlin</testSourceDirectory>

    <plugins>
      <plugin>
        <groupId>org.jetbrains.kotlin</groupId>
        <artifactId>kotlin-maven-plugin</artifactId>
        <version>${kotlin.version}</version>
        <executions>
          <execution>
            <id>compile</id>
            <phase>compile</phase>
            <goals>
              <goal>compile</goal>
            </goals>
          </execution>
          <execution>
            <id>test-compile</id>
            <phase>test-compile</phase>
            <goals>
              <goal>test-compile</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
  </build>

... But this was in a multi-module Maven project where modules were either Java sources only or Kotlin sources only - never mixed within one module. Note sure if that's significant.

[Greg]

@mihakrajnc Oh, and for the Kotlin source formatting, could we please follow the official Kotlin style guide.

[Miha Krajnc]

@gkopff Perfect, I think IntelliJ set up something similar when it added Kotlin support automatically, with mixed java / kotlin files. I'll figure out what's needed and what's not, thanks!

For formatting, of course, official style guide. I'm not a monster :)

And I'll just route the extension calls through the Converters class so we don't duplicate the code, and add a test for it that basically does the same thing you do for the Converters class test testRegisterAll.

P.S. For a moment I thought of naming the Kotlin converters file Konverters.kt.... but thought better of it :)