Thursday, 19 November 2009

Future Directions for C# and Visual Basic

I’m having great fun watching the Microsoft PDC 2009 session videos, and blogging the highlights for future reference. In case you want to jump into the video, I’ve included some time-checks in brackets (0:00). Read the rest of the series here.

Luca Bolognese opened his session Future Directions for C# and Visual Basic by announcing that the strategy for future development of C# and Visual Basic is one of co-evolution. As he said, the previous strategy where each language was independent, and one would get new features that the other didn’t was “maximising unsatisfaction”. Now there is one compiler team responsible for both languages, and any big new features added to one will get added to the other. VS 2010 already brings the two languages much closer together, and this will increase in the future.

In the first half of the presentation, Luca talked about the three big trends in current languages: Declarative, Dynamic and Concurrent.LanguageTrendsIn a demo (starting at 6:20 in the video) Luca created a CSV file parser. He showed (12:08) how writing the code in declarative style (using LINQ) not only makes it easier to read, it also makes it easier to parallelize. As simple as adding AsParallel() to the middle of the query in fact (15:18). The Task Parallel Library (part of .Net 4) makes it possible to parallelize imperative code (for loops, etc.) but with much greater potential for bugs like unsynchronized collection access (16:20). Luca then went on to demonstrate the dynamic language features in C# 4, and the DynamicObject base class (24:38).

Then he turned to the future, but not without a disclaimer that there were no promises of anything he talked about actually shipping. It seems, however, that Microsoft are pretty firmly committed to the first item he mentioned: rewriting of the C# compiler in C# and the VB.Net compiler in VB.Net, and opening up the black box so that we can make use of the lexer, parser, code generator, etc. From what he said later on, I gather that most of the team are currently involved in completing this work.

Luca demonstrated (36:00) how in just 100 lines of code he could use the new APIs to create a refactoring that would re-order the parameters of a method (and take care of the call site). Previously, anyone wanting to do something like this would have first needed to write a lexer and a parser, but that would be provided for us.


The last demonstration was of something Luca called “resumable methods”. These appear to be something akin to async workflows in F#. By prefixing an expression with the “yield” statement, Luca indicated to the compiler that he wanted the method to be called asynchronously (50:30). The compiler then takes care of rewriting the code so that execution resumes at the next statement once the asynchronous execution of the first statement completes. The benefit of this is that the thread can be used for something else meanwhile. By getting the compiler to do the rewriting we can avoid a whole lot of ugly code (see the video at 46:24). ResumableMethodsImplementationOne other thing that Luca mentioned is being considered by the team is support for immutability (52:41) . He said that they had considered 4 or 5 different designs but hadn’t yet settled on one that was exactly right. Part of the problem is that so much of the language is affected: not just the types themselves, but parameters, fields, etc.

If you want more on this, read Sasha Goldstein’s account of Luca’s talk.


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