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The //* /*/ //*/ comment toggle trick

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DISCLAIMER: This is a trick. Do not adopt this trick in production code. Use it wisely while you're doing proof of concept and the like.

So, I guess I'm not the only one that need some way of easily toggling code in and out of the code.

This trick below can be used to toggle between two sets of code, with one symbol in the code with no additional short-keys to learn, and no tool dependencies!

//*                      /*
someCode();              someCode();
/*/                      /*/
someOtherCode();         someOtherCode();
//*/                     //*/

Here is a version for simply commenting code in and out:

Activated:

//*
someCode();
//*/

Deactivated / commented out:

/*
someCode();
//*/

Comments

  • Blank-mugshot
    ralphholzmann

    Nice! I've used a similar method in JavaScript like this:

    // On!
    /**/
    var foo = "bar";
    /**/
    
    // Off!
    /** /
    var foo = "bar";
    /**/
    

    The trick is to toggle the space after the second asterisk in the first multiline comment block. Interesting to see other ways to do this as well!

  • Blank-mugshot
    wildlyinaccurate

    A much safer alternative is to use feature flags - http://code.flickr.net/2009/12/02/flipping-out/

  • Blank-mugshot
    ricordel

    Nice trick, thank you for sharing ! One little reserve: at least in C, this fails if the code to toggle contains comments itself:

    //*
    spawn_unicorns();
    /*/
    slay_the_unicorns(); /* FIXME: This function kills unicorns ! */
    launch_missile();
    //*/
    

    In this code, you won't kill unicorns, but you will always launch a missile, which is not what was intented. It only works in C/C++, but I tend to prefer:

    #if 1
    spawn_unicorns();
    #else
    slay_the_unicorns(); /* FIXME: please don't to that. */
    launch_missile();
    #endif
    

    You just have to change "1" to "0" to toggle between nice and evil code, and it has no restriction regarding embedded comments.

    That said, I'll remember your solution for Java, Javascript and others.

  • Blank-mugshot
    brycec

    I just sat in sublime text for like 15 minutes with my mouth agape as I typed forward slash and backspace over and over, watching the syntax highlighting flip back and forth with each keypress. This is beautiful.

  • Blank-mugshot
    alexanderbrevig

    @wildlyinaccurate feature flippers do not prevent code from being built, and thus the code is available in the binary. What's safest depends on the definition of save, and the specs of the project. Feature flippers solves a problem (highly relevant to the open/closed principle) but not the problem this trick solves.

  • 35862cd
    benaston

    I wouldn't normally comment, but this has a lot of people looking at it. Don't do this. For reasons why, see the hacker news thread https://news.ycombinator.com/item?id=5625490

  • Blank-mugshot
    benjamw

    I agree that commented-out code should not be part of production code.

    But I use this trick all the time while writing/debugging/updating/fixing code.

    It makes enabling/disabling code blocks extremely quick and easy.

  • Blank-mugshot
    mihaimaruseac

    I came to mention the #if 0 version only to find that it was already mentioned. Too bad it doesn't work in other languages as well :(

  • Blank-mugshot
    alexanderbrevig

    @mikbe you should never work on production code with this trick. Then someone is doing something wrong. This is just a trick that's fun to use while testing out two different approaches. Such as an iterative versus a recursive algorithm.

  • Blank-mugshot
    alexanderbrevig
  • Blank-mugshot
    cguillemette

    What editor are you using?

  • Blank-mugshot
    alexanderbrevig

    @cguillemette I'm using 8 editors, Visual Studio, Sublime Text 2/3, Mono Develop, Notepad++, Eclipse, NetBeans, MS SQL Management Studio and Vim.

  • Blank-mugshot
    praetor_alpha

    oh god. this is what my old company used to control database connections. jdbc in development (tomcat) and jndi lookup everywhere else (websphere i think?). yes, we had to modify code to move to another environment! I couldn't explain this enough to my manager that this was a bad thing.

    that was the least of the issues. it was on the whole, written by people who didn't know how the hell to use java. (probably former SQL devs?)

  • Blank-mugshot
    openist

    I just have a shortcut in emacs that comments and uncomments things in all languages seamlessly.

  • Blank-mugshot
    nekwebdev

    Sublime text 2 also does that by default :)

  • 0_qom0aduhb-oqe3kjqai8awfwuts9ocnjxes8ae0vkqm6z6_go2w1xowuvxddw5vabdu3oddzl5ac
    mrjavascript

    @ralphholzmann Super-slick trick!

  • Blank-mugshot
    mikbe

    I would hate having to work on code with this trick. It would be hugely confusing.

    I accept that your probably a lot smarter than me so have no problem with it but I always strive to write code like other people are going to read it. Part of that is not writing cleverly so much as writing clearly.

  • Me_normal
    mikeheaver

    Nice to see it published...but this trick has been around for a quite a few years now.

  • Me_normal
    andyswaff

    I see no issues with this as long as you don't check it in or deploy to production like this. For local/debug development, this can be quite useful. If you need a reminder, you could add a commented line with a reminder (like "TODO: remove toggle") and do a Find before checking in.

  • E7426a813d3bab6b1758f06c44fe0f4b
    blaxus

    I also have been doing this PHP. @ralphholzmann's version is a better one in my opinion, because it can be used multiple times after each other. Allowing you to toggle multiple stacks.

  • Blank-mugshot
    mnafricano

    @nekwebdev Sublime Text 2 is the best, but Brackets is definitely close behind! I love Brackets so far but JSLint pisses me off, haha. If you haven't tried Brackets out yet, I strongly suggest that you do: http://brackets.io/

  • Blank-mugshot
    chridal

    This one is awesome!

  • Blank-mugshot
    alland

    is it really hard to cmd-slash ?

  • ___-1____normal
    obd2works1

    I see no issues with this as long as you don't check it in or deploy to production like this. http://www.obd2works.com/

  • Blank-mugshot
    rafaelrinaldi

    For those writing JavaScript with r.js compiler, pragmas can be very useful for this kind of thing.

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