Before I get into the subject of today's post, thanks so much to all of you who have given us great feedback on the Roslyn CTP. Please keep it coming . I'm definitely going to do some articles on Roslyn in the future; the past few weeks I have been too busy actually implementing it to write much about...

(This is the fourth and final part of a series on the corner cases of optional arguments in C# 4; part three is here .) Last time we discussed how some people think that an optional argument generates a bunch of overloads that call each other. People also sometimes incorrectly think that void M(string...

(This is part three of a series on the corner cases of optional arguments in C# 4; part two is here . Part four is here .) A lot of people seem to think that this: void M(string x, bool y = false) { ... whatever ... } is actually a syntactic sugar for the way you used to have to write this in C#, which...

(This is part two of a series on the corner cases of optional arguments in C# 4. Part one is here . Part three is here . This portion of the series was inspired by this StackOverflow question .) Last time we saw that the declared optional arguments of an interface method need not be optional arguments...

(This is part one of a series on the corner cases of optional arguments in C# 4. Part two is here .) In C# 4.0 we added "optional arguments"; that is, you can state in the declaration of a method's parameter that if certain arguments are omitted, then constants can be substituted for them: void M(int...

Today, another question from StackOverflow , and again, presented as a dialogue as is my wont. The MSDN documentation for List<T> says that the class is declared as public class List<T> : IList<T>, ICollection<T>, IEnumerable<T>, IList, ICollection, IEnumerable Does List<T>...

Before we get into today's topic, a quick update on my posting from last year about Roslyn jobs. We have gotten a lot of good leads and made some hires but we still have positions open, both on the Roslyn team and on the larger Visual Studio team. For details, see this post on the Visual Studio blog...

A brief digression from C# 5 to talk about C# 4: the annotated C# 4 specification is now available in book form from Addison-Wesley . It is of course handy to have a specification in book form, particularly if you're going to while away the hours with the book sitting by a warm fire. (It's hundreds of...

Earlier this year I was the technical editor of " Teach Yourself Visual C# 2010 in 24 Hours " by Scott Dorman, and I am pleased to announce that it is available in stores now. Scott has pretty much completely rewritten this from the previous edition to ensure that it is totally up-to-date for C# 4. If...

Good heavens, I just realized I completely forgot to post a link to this interview . I'm a year late, but better late than never. A year ago Ken stopped by my office and we had a very freewheeling, entertaining and rather random conversation about many diverse aspects of programming language design...

My copy of Essential C# 4.0 just arrived, and it looks great. I was one of the technical reviewers of this book. Some books are a pain to edit, but the Essential C# series is one of my favourites. It totally lives up to its name; it really does give you lots of essential information for developing high...

As I’m sure you know by now, we are done implementing C# 4. We’ve added support for interoperability with dynamic languages and legacy object models, named and optional parameters, the ability to “link” against interfaces from a Primary Interop Assembly, and my favourite feature, covariance and contravariance...

Large bodies of code written in the C/C++ languages typically divide up the code into “header” files, which are just declarations of methods and types (and definitions of macros). The actual bodies of those methods and types are in completely different files. People sometimes ask me why doesn’t C#...

I thought it might be interesting for you all to get a precise description of how exactly it is that we determine when it is legal to put "in" and "out" on a type parameter declaration in C# 4. I'm doing this here because (1) it's of general interest, and (2) our attempt to make a more human-readable...

I've written a lot about this already, but I think one particular point bears repeating. As we're getting closer to shipping C# 4.0, I'm seeing a lot of documents, blogs, and so on, attempting to explain what "covariant" means. This is a tricky word to define in a way that is actually meaningful to...

Interestingly enough, no one correctly guessed why I needed code in the compiler to transform a method argument list into a form that batched up the side effecting expressions, stuck their values in variables, and then called the method with the side-effect-free variable references. There certainly were...

Somehow it has happened again; people just keep on recording videos of me and putting them on the internet. In these videos you find out what I look like when lit from above and behind. Kinda spooky. We should have made the room entirely dark and held a flashlight underneath my face. That would be...

I'm frequently asked "you guys added extension methods to C# 3, so why not add extension properties as well?" Good question. First, let me talk a bit about C# 3. Clearly the big feature in C# 3 was LINQ. In a sense we had only three features in C# 3: everything necessary for LINQ -- implicitly...

Because I'm a geek, I enjoy learning about the sometimes-subtle differences between easily-confused things. For example: I'm still not super-clear in my head on the differences between a hub , router and switch and how it relates to the gnomes that live inside of each. Hunks of minerals found...

Many programming languages, C# included, treat certain sequences of letters as “special”. Some sequences are so special that they cannot be used as identifiers. Let’s call those the “reserved keywords” and the remaining special sequences we’ll call the “contextual keywords”. They are “contextual” because...

Suppose you’ve got a sequence of Foos and you want to project from that a sequences of Bars. That’s straightforward using LINQ: IEnumerable<Bars> bars = from foo in foos select MakeBar(foo); or, without the query sugar: IEnumerable<Bars> bars = foos.Select(foo=>MakeBar(foo));...

A couple years ago I wrote a bit about how our codegen for the lock statement could sometimes lead to situations in which an unoptimized build had different potential deadlocks than an optimized build of the same source code. This is unfortunate, so we've fixed that for C# 4.0. However, all is still...

When we're designing a new version of the language, something we think about a lot is whether the proposed new features "hang together". Having a consistent "theme" to a release makes it easier for us to prioritize and organize proposals, it makes it easier for our marketing and user education people...

Mads, Chris, Sam and me on Channel Nine. Enjoy.

Amazingly enough, it has happened again . Why does this keep happening to me? Anders, Mads and Eric on C# 4.0: C# 4.0 with Anders Hejlsberg, Mads Torgersen, and Eric Lippert - Part 1 of 2 C# 4.0 with Anders Hejlsberg, Mads Torgersen, and Eric Lippert - Part 2 of 2 Anders, Mads and Scott on...