Throwing the Big Switch on Roslyn (Matt Gertz, VS Managed Languages Development Manager)

Throwing the Big Switch on Roslyn (Matt Gertz, VS Managed Languages Development Manager)

Rate This
  • Comments 43

So, the entryway to my house has eight light switches along the wall.  Two of them control the porch lights, and another two work the same entryway light (despite the switches being only a couple of feet apart).  I haven’t the foggiest idea what the rest of the switches do.  I’ve been scared to try them out, actually.  (I worry that one day I’ll accidentally throw one of them and find out later that my couch is missing or something odd like that.)

However, I am pleased to announce that we’ve turned on quite a different switch here on the Managed Languages team, with very successful results!  As many of you know, we’ve been diligently working on a replacement for our VB & C# compilers (and certain IDE pieces that leverage them) which is code-named “Roslyn.”  Roslyn introduces a far more open model for compilation, which will allow developers to reach inside the compiler itself and see the world (or, at least, solutions and projects) as it does; this, in turn, will lead to far richer IDE and diagnostics being able to be developed at considerably reduced effort and cost. 

And now, we’ve turned on The Big Switch in the Visual Studio organization and turned on Roslyn!

The Big Leap Forward

Specifically, I’m pleased to announce that everyone in the Visual Studio organization is using Roslyn in their daily work now.  In fact, the daily builds of VS are now compiled using Roslyn, all as part of a process that we refer to in the biz as “dogfooding.” 

Now, this change wasn’t trivial and, as with the mysterious light switches in my entryway, there was a lot of caution involved before we got to the point where Anders ceremoniously turned on the switch and enabled Roslyn for the division.  Although we are part of the Visual Studio org, in many ways the rest of the VS org is like a customer to us as well, and so we had to be really careful not to derail any teams in our enthusiasm to reach this milestone.  (For some reason, the other teams feel that their work is important, too… go figure.) 

So, earlier this year, we engaged the toughest bunch of critics we could find (that is, the other VS test teams), and asked them to do several weeks of hard-core tests against their code – essentially, every test that they already had plus new ones specifically designed for this situation.  At the same time, we ran and re-ran all sorts of performance tests to ensure that we wouldn’t be slowing down either developers or our build lab.  We did a walking tour of the rest of the org and got them educated on the changes that Roslyn would bring.  We compiled & assessed over 60,000 projects, large and small, both internal and external to Microsoft (including flagship Microsoft products).  We fixed whatever blocking bugs we found as a result of all of that and then, at the end of October, we switched the entire division to using Roslyn bits.  I’m happy to say that all that prep work set up us well – since The Big Switch, we’ve run into no major issues! 

So… you’re done?

Not quite.  “Dogfooding” is a prelude to being done, but there’s still a bit of polish to put on before the new code is truly complete.  Nevertheless, we are at the state where Roslyn is highly usable for daily work.  It’s a huge milestone and essentially says that we’ve turned the corner.  There’s no going back now!

So, then, when can we see it?

As you may know, our last generally-available preview for Roslyn was September 2012.  No, that year is not a typo.  Yeah, we do feel a bit embarrassed about that.  Yes, we’ve been a little quiet.  No, there was nothing wrong going on here, things were actually going extremely well, it’s just that we’ve just been really heads’ down and focused on The Big Switch and…

Oh, to heck with the excuses, and let me just tell you what we’re doing. 

Now, of course, I can’t ever reveal shipping plans in a casual blog post like this, because I want to keep my job that’s someone else’s story to tell.  However, if you can keep a secret, I’ll tell you this much:  we’re now actively working through the details on starting up regular previews again.  The code is in a really nice state these days, and we can hardly wait to show you what we’ve been up to as we’ve been solidifying Roslyn!  (But don’t tell anyone that I told you.  This is just between you and me.) 


We wish you all the best for the New Year – 2014 is going to be an exciting year for us all vis-à-vis Roslyn.  We’re delighted to have you along with us on the journey! 

‘Til next time,


Leave a Comment
  • Please add 4 and 1 and type the answer here:
  • Post
  • I want to share the link of this project that use Roslyn: QInjection on CodePlex.

    The link:

  • My code compiles just fine today....

  • Can you please release NuGet packages first?

  • Now that the holidays are over, can we get the dates. Please... Pretty please...

    Why all the secrecy around CTP release schedule?  These are just previews no?  Most people don't expect production level stability.

  • "Why do I want it?"

    from the language team side.

     "new compiler structure modernizes the compiler making it easier to maintain and add new

      features going forward."

     for day to day use, it compiles the old code the same.  Except now not every vendor or that matter Microsoft unit that works with the language has to rewrite the compiler to work on the language.  

    Resharper and it ilk, come to mind. fxcop, code contracts on the MS side.

    and Repl for C#. that in and of itself, makes this a worthy upgrade, and getting all the other stuff is gravy. even better is the Repl has full syntax and error reporting.  

    C# as a scripting language.


  • Wpf+Roslyn+Sql server = sistemas abiertos, enviar mail y envio un gran ejemplo de roslyn

  • That is a fricking torment you are doing right here, right now.

    Not to mention that I read this already a month and a half forward.

  • It's been almost 2 months now since this posting, so I thought I would ping to check if there was any news.  I was hoping to see more transparency since this announcement.  It is 7 weeks to the day until Build 2014.  Do we have to wait to hear something then or can you at least let us know if we will be getting some good news/bits before then (or even then).

    Thanks.  Hope to hear from the Roslyn team in the not-so-distant future.

  • For anyone that hasn't heard the video, F#'s compiler was already written in F#. So it shouldn't be very difficult at all to get Roslyn going on it.

  • Is Roslyn meant to be part of the .net framework or will it just be available in Visual Studio? (i.e. is it meant to be used to provide scripting capabilities to any application build in C# or just to Visual Studio)?


    I created a system using roslyn, which allows me to create desktop application with WPF + C # + Sql Server Azure and allow midificado be at runtime.

    if you are interested in trying this system, write to the mail.

    wilmer.barrios @

  • Hey,

    I see that the project is now open source:

    What does it mean regarding the next release or how does it coincide with the above?

  • Very nice !

Page 3 of 3 (43 items) 123