Luke Hoban: Orcas - Compiling LINQ, C# Futures, Intellisense | Going Deep

Meet Luke Hoban, Program Manager on the C# Compiler team. Here, we talk about how LINQ works, from a compiler point of view. As you know by now, LINQ is a construct that is built of new language level innovations which of course must have compiler support... As you might imagine, given the nature of LINQ's requisite language level components, we talk about functional programming and it's new role in our good old imperative world. In Orcas, you shouldn't talk about LINQ without showing it in action inside of Visual Studio.

Enjoy.

For the detail-oriented folks out there: I shot this interview a few months ago, so you'll hear references to the Feb/March CTP. Have no fear, Niners, the content in this interview is as pertinent now as it was then (even more so with the release of Orcas beta 1).

Follow the Discussion

Follow
Oops, something didn't work.

Try again?

Sign In to be begin to follow these comments

What does this mean?
Following an item on Channel 9 allows you to watch for new content and comments that you are interested in. You need to be signed in to Channel 9 to use this feature.

Getting "follow" information

Stop following these comments

Start following these comments

What does this mean?
Following an item on Channel 9 allows you to watch for new content and comments that you are interested in and view them all on your notifications page.

Removing your "follow"

Setting up your "follow"

Did you know you can
sign up for email notifications?
- Subscribe to this comments

raghur

May 17, 2007 at 8:49 PM

Charles,

At the begining of the program, you mentioned "February CTP". Did I hear you right? If so, is this old video? I have not gone through the whole video yet.

Thanks.
Raghu/..
raghur

May 17, 2007 at 8:50 PM

Sorry. I should have read your comment. You did mention that it was old video.

Raghu/..
Jsoh :::Windows 8 Style UI :::

May 17, 2007 at 9:24 PM

Way to go Charles, @ 18:10 whipping out the Distinct keyword! I really have to sharpen-up my linq skills. When I first used Orcas, I was disturbed how aggressively intelisense was in investigating my code. However, it saves a tremendous amount of time, which would otherwise be wasted staring at a blinking pipe. The results of better integration between the IDE and the compiler are truly impressive.
Chadk excuse me - do you has a flavor?

May 18, 2007 at 1:51 AM

A young dude doing that kind of cool stuff. Respect!
Tank

May 18, 2007 at 6:13 AM

Great video!

I love the "simplicity" of LINQ and now I think it's even simpler after listening to Luke's explanations.

Would be nice if you could make a video where it's showed how to make a simple LINQ-to-X interface, since, I think, that where the real power of LINQ is unleashed

- Dan
littleguru <3 Seattle

May 18, 2007 at 9:59 AM

Chadk wrote:

A young dude doing that kind of cool stuff. Respect!

Damn! I want to get the internship next summer! I want to work and chat with you guys...

Great video, Charles - although you could have dug a little bit deeper - but it's hard when you see something for the first time.
RoyalSchrubber One. How many time travellers does it take to change a lightbulb?

May 18, 2007 at 11:30 AM

Nice video.

If anybody know, I would be very thankful if someone could explain me speed implications of the LINQ.

I've watche the video and it seems LINQ uses a lot of lambda functions, which I suspect are stack based. So are the linq expressions as fast as normal hand coded loops or they abuse stack and are thus slow. Can JIT compiler/Linq somehow inline those lambda functions to avoid suffering from stack over-use?

Or in other words, can I use linq for some serious math computations as a replacement for 'while' and 'for' statement?

Thanks for any answers.
SealedSun

May 19, 2007 at 1:56 PM

Inlining probably won't happen, because the JIT compiler would have to inline all the .Where, .Group, .Sort and .Select calls and those are definitely not short functions.
Apart from that, LINQ over in-memory structures is written against interfaces (if I'm not mistaken) and therefor uses virtual calls all over the place.
And yes, the lambda expressions are called via delegates.
littleguru <3 Seattle

May 20, 2007 at 2:28 PM

SealedSun wrote:

Inlining probably won't happen, because the JIT compiler would have to inline all the .Where, .Group, .Sort and .Select calls and those are definitely not short functions.
Apart from that, LINQ over in-memory structures is written against interfaces (if I'm not mistaken) and therefor uses virtual calls all over the place.
And yes, the lambda expressions are called via delegates.

Hmmm. The .Where, .Group, .Sort, ... methods are defined in static classes (the in memory that come with .NET 3.5 - Enumerable is the static class name) and therefore in static methods. I think they can be inlined without any problems (They are also not that long, because they return only an IQueryable instance). The lambda expressions itself are very short and good candidates for inlining.

I wonder if somebody from the team could jump into this discussion and bring some light to it.
bdesmet Bart De Smet [MSFT::SQL::CloudProgrammability::Rx]

May 23, 2007 at 8:32 AM

People who'd like to build building custom query providers for LINQ using the IQueryable interface might be interested to check out my blog series on LINQ to LDAP. Another interesting project might be LINQ to SharePoint on CodePlex. If you want to get some insight in the standard query operators from LINQ to Objects, check out the LINQ-SQO project.

Just my 3.14 cents.

-Bart
senthilkumar

May 26, 2007 at 2:25 PM

Apart from type inference of parameters, what do lamba functions add to anonymous methods? In the example Luke showed on the whiteboard, instead of generating array.Select( i => i*i), the compiler could have generated array.Select(delegate (int i) { return i*i;} );. Of course, it would have to know at that point that i is an int, but it would have to know about it eventually, even with lambda functions. I guess it makes the compiler design simpler to do it in two separate steps?
Luke Hoban

Jun 04, 2007 at 8:31 AM

I'd say lambda expressions have two major benefits over anonymous methods. First, they are syntactically more concise. Since the functions defined by lambdas or anonymous methods are most often needed in-line as part of a larger expression - it's important to have a good concise syntax. Otherwise, the code quickly becomes very difficult to read. So a major goal for lambdas was to provide a really concise and readable way to declare these small functions in-line.

The other benefit is the type inference you mention. This also helps with conciseness - but more importantly it avoids littering the type names all over a single simple expression, which can become a significant syntactic issue for many uses of lambdas.

At a higher level - the emphasis on lambdas is actually much more general than LINQ. We see many new APIs looking to provide the kind of level of abstraction that really requires taking delegates as arguments - and LINQ is just one example. I definitely expect to see more of these APIs in other interesting domains over the coming months/years.