CodeCampTalk-2010.ppt

1. Incorrect errors when you open a solution with breakpoints in .aspx.cs files.
2. Incorrect errors regarding conversions of constants in rare cases.
3. An issue importing metadata from some non-C# assemblies.
4. Some timing issues where errors would appear and then disappear during typing or file/solution opening.

We spent some time analyzing the issues, and we’ve come up with a hotfix to address them.  If you’re seeing any issues where you get live semantic errors that you don’t expect, please download this fix and try it out.

Let me know if you find any issues with it!

Thanks!

void RemoveSomeElements(Dictionary<string, int> dict)
{
    foreach (var e in dict)
    {
        if (e.Value < 35)
        {
            // Remove e!
        }
    }
}

Several people replied that he could just create a list of elements to be removed and then iterate that afterwards:

var keysToRemove = new List<string>();
foreach (var e in dict)
{
    if (e.Value < 35)
    {
        keysToRemove.Add(e.Key);
    }
}

foreach (var key in keysToRemove)
{
    dict.Remove(key);
}

That works, but it’s pretty verbose.  Someone suggested a more functional way to do it that’s pretty nice:

dict.ToList().Where(pair => pair.Value < 35).ToList().ForEach(pair => dict.Remove(pair.Key));

At this point I decided to show off, and make it more efficient by using an “Apply” extension method instead of the .ForEach method that shipped on List<T> in .Net 2.0.  I came up with this:

dict.Where(pair => pair.Value < 35).Apply(pair => dict.Remove(pair.Key)).Apply();

Along with the code to Apply:

public static class ApplyExtensions
{
    public static IEnumerable<T> Apply<T>(this IEnumerable<T> source, Action<T> action)
    {
        Argument.NotNull(source, () => () => source);
        Argument.NotNull(action, () => () => action);
        return ApplyInternal(source, action);
    }

    internal static IEnumerable<T> ApplyInternal<T>(IEnumerable<T> source, Action<T> action)
    {
        foreach (var e in source)
        {
            action(e);
            yield return e;
        }
    }

    public static void Apply<T>(this IEnumerable<T> source)
    {
        foreach (var e in source)
        {
            // do nothing, just make sure the elements are enumerated.
        }
    }

}

Here I thought I was doing right by C# 3.0, and showing people how to use lazily chained iterators.  Unfortunately, this code drops us right back to the original problem!  Because of lazy iteration, we’re actually still iterating the dictionary when we try to remove the elements, and so we invalidate the first iterator in our chain. 

It’s a simple fix, but still a reminder that the semantics of delayed execution can be tricky to reason about sometimes:

dict.Where(pair => pair.Value < 35).ToArray().Apply(pair => dict.Remove(pair.Key)).Apply();

The “ToArray” call finishes the iteration of the dictionary, but uses less space than the original “.ForEach” solution, since we only realize a collection of the elements to be removed, instead of all of the elements in the dictionary.

While playing with expression trees, a while ago I came up with this:

public static class Argument
{
    public static void NotNull(object value, Expression<Func<Func<object>>> arg)
    {
        if (value == null)
        {
            var body1 = (Expression<Func<object>>)arg.Body;
            var body2 = (MemberExpression)body1.Body;
            throw new ArgumentNullException(body2.Member.Name);
        }

    }
}

You can use this for argument validation like this:

static void Main(string[] args)
{
    Argument.NotNull(args, () => () => args);
}

This looks a little strange, but has some interesting properties:

1. There are no strings, which means that refactoring tools “Just Work” and update all references.
2. The majority of the reflection code happens only in the exception code, which means that this has significantly better performance than my first attempt (which took just an “Expression<Func<object>>”

On the other hand it has some drawbacks too:

1. The calling side looks a little strange with “() => () =>'”
2. Using this approach will lead to a LOT of compiler generated display classes to store the parameter references.

I’m not sure I would use this in production code, but it was an interesting exercise to come up with a way of validating parameters that doesn’t involve strings.

What do you think?

On my host machine, it takes about 8 minutes to do a clean build of the code I usually work on.  With my previous virtual machine, it took about 32 minutes!  I think this happened because while my host machine has 4 processors, the VM can only access one of those.  I wasn’t willing to pay that price.  With HyperV today it takes about 9.5 minutes, and I am willing to pay that price for the added flexibility and the time I can save installing builds.

In order to do work in three different branches somewhat simultaneously, I need to have test machines that have those three different branches installed.  It wasn't reasonable to re-image and re-install my single test machine every time I needed to switch branches.  It's also not very cost effective for me to have 3 test machines where two of them spend the vast majority of their time idle, not to mention that this doesn't scale well if one day I need a 4th branch.

So last week, I jumped on the virtualization bandwagon.  I flattened my best machine, installed windows server 2008 64-bit*, and started using virtual machines for my test machines.  So far it's been working out very well for me, but I do have to give credit to some other people.  A few people in our test group have written some automation around Virtual Server to make life easy for people wanting to use virtual machines.  They have some software that manages creating VMs for you.  It basically does the following steps:

1. Pull an image of a selected OS from the network, and cache it locally.
2. Create a VM
3. Install the OS
4. Add it to the corporate network domain
5. Install the latest set of Windows Updates
6. Add my domain account to the Administrators group.
7. Optionally run a custom script to install more software.

For step 7, this group has provided stock scripts for installing various versions of Visual Studio, and one to install the latest build from a selected branch.  It's really convenient, since steps 2 to 6 only take about 25 minutes (and step 1 is usually skipped because the image is in the usually in your local cache).

They also have an option to have the VM be destroyed and re-created every night, which means that you can come in to work in the morning and have a fresh test machine with the latest build on it.

So, I started out need to have 3 test machines in 3 different branches, but the system is so easy to use that I've already built up a larger set than that.  My current list of virtual machines is:

1. VS2008 without SP1
2. VS2008 with SP1.
3. A debug build of VS from each of the 3 branches I mentioned above.
4. A release build of VS from the branch I normally work in for performance testing (I don't need absolute numbers, just finding the hotspots).

My only wish is that they update it to take advantage of Hyper-V soon to improve performance of the hosted machines.

* I previously had Vista 32-bit on the machine because at the time I set it up Server 2008 wasn't released yet, and there was a bug in the interim builds of visual studio that made install fail on 64-bit machines.

Also, I've changed roles a bit.  I'm now the dev lead for the C# IDE team, instead of an individual contributor on the team, so I'm learning what it's like to be a people manager.

I have a few ideas queued up for future blog posts, but I'm definitely interested in your questions too.  What parts of features in the C# editor are you curious about?  What about work at MS and our processes, is that a topic of any interest?