The documentation for Kotlin is now located on the new site. This page is kept for historical reasons
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The documentation for Kotlin is now located on the new site. This page is kept for historical reasons

Note: If you've come to this page from an external link, please start reading at the Welcome page, not this one.

Project Kotlin was born in Saint Petersburg, Russia, where one of the main JetBrains' development offices is located. Kotlin is the name of an island situated nearby Saint Petersburg, in the Gulf of Finland, with a beautiful town of Kronstadt build upon the island. The current logo was inspired by the probably imagined connection of the word "Kotlin" with the word "Kettle", which was originally mentioned in the 1911 edition of Encyclopedia Britannica.

Disclaimer 1: We believe that no coffee or other exotic cultures are grown in Kotlin in any noticeable quantities.

Disclaimer 2: Despite the fact that Kotlin Class Destroyers were named after the same island, our language is not intended for class destruction by any means.

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  1. Jul 21, 2011


    I'd change the colors, though. Looks like a Google language to me :)

    1. Jul 22, 2011


      Totally agree.

  2. Jul 24, 2011


    Hm, the name "Kotlin" sounds very unpleasant to me.

    But I like the language the more... can't wait to write some real code in it, so please hurry on :-)


    1. Jul 25, 2011


      In German, Kot = Shit, and Kutteln (which sounds similar) is tripe (this is how it looks: Trippa.jpg)

  3. Jul 25, 2011


    You shoud be thinking... One more language !?!?!

    But It's always a good idea!!!

    I agree....

  4. Jul 28, 2011


    Hurry up guys!  I want to play with it!! :)  Ignore all the Scala dudes complaining how it's like Scala.  If it was like Scala, only wankers would be interested.

  5. Aug 23, 2011

    It may be been said elsewhere but deserves repeating.

    Thank you for the best practices, Effective Java and motivation references.  It is a delight to see the thinking behind your designs.  I expect Kotlin to be used as a CS case study for language design; your reasoning is explicitly stated.

    1. Aug 24, 2011

      Thanks for your kind words.

  6. Aug 25, 2011


    Is there any news about this project? I hope I can try it as soon as possible, I can't wait

    1. Aug 25, 2011

      It's not too long to wait. We plan a public Beta by the end of the year.

      Meanwhile, you can watch our progress in the blog and twitter.

      1. Aug 30, 2011


        Can't await the end of this year! The language looks pretty balanced to me. Godspeed!

        1. Aug 31, 2011

          Thanks for your kind words

  7. Sep 02, 2011


    Also can't wait for it to come out. Looks nice!

  8. Sep 07, 2011


    Kotlin is also best Polish ketchup made in the city with the same name.

  9. Oct 25, 2011


    Can you compare it also with gosu(, phantom ( and grovy++ (

    1. Oct 25, 2011

      I guess, the community will provide a detailed comparison at some point. Some quick highlights:

      How Kotlin differs from Gosu:

      • one can compile a program and distribute binaries (Gosu only compiles on-the-fly).


      • Kotlin has user-defined generic types and functions

      Groovy++ is a very nice demonstration of how much you can do if you want to turn a dynamic language into a static one. Kotlin is inherently statically typed.

  10. Nov 28, 2011


    Thanks guys, it's a great puzzle gathered from Scala, Groovy, C# and Java! I think it is yet not late to do a little research regarding the meaning of word "Kotlin" in other languages and the coloring of the logo which really resembles the ones from google..

    Wish your language become popular! 

    1. May 13, 2012

      When Kotlin .NET backend will be implemented? How can I speed up this process? :)

      1. May 22, 2012

        We didn't start working on this yet. You can speed it up by contributing the implementation

        1. May 24, 2012

          I'm ready to try, what should I do first? Please feel free to contact me by e-mail in Russian.

          1. May 24, 2012

            You can have a look at how the Java and JS back-ends work, and implement your own back-end for .NET.
            I think, the first step would be to find a Java library that would allow you to emit IL and try to use it independently from Kotlin. When that works, you can start to translate simple Kotlin constructs taking inspiration from our existing back-ends.

            Please feel free to ask questions in forums or contact me personally by email: andrey.breslav jetbrains com

  11. Feb 21, 2012

    sounds a bit like Dart... do you think you can stand against Google's new&mighty VM language?

    1. Feb 21, 2012

      Do you think Google's yet another VM language can stand against new&mighty initiative from Jetbrains?

    2. Feb 22, 2012

      I think we fit very easily into the same world

      1. Feb 22, 2012

        True. From my point of view, Kotlin is especially important to JetBrains as that's the way to bring IntelliJ (with it's huge JVM/Java code base) to the browser.</speculation>

        I'll write some additional server-side parts of my GWT app in Kotlin as soon as its production-ready. I've done the same thing with  Scala two years ago and it was a mess: Scala doesn't play nicely with Java as soon as Java's language constructs become complex. I've read that you've addressed this problem in Kotlin as "(strong?) compatibility".

  12. Jul 26, 2012

    Is there some extension functions for encapsulate List<T> as Iterable (for example, asIterable()) ? 

    and is there extension functions for Iterable same as in C# for IEnumerable (class Enumerable)?

    1. Jul 27, 2012


      1. Jul 27, 2012

        where can I read something about it?

        1. Jul 27, 2012

          Currently it's only in the source code of the standard library. It is available here:

          1. Jul 27, 2012