Krzysztof Cwalina

Talk: A .NET developer's view of Windows 8 Metro style app development

Krzysztof Cwalina — Wed, 21 Sep 2011 00:50:00 GMT

I just came back from BUILD where I gave a talk about a new .NET profile that managed developers will be using when writing Windows 8 Metro style apps. You can watch the video at http://channel9.msdn.com/Events/BUILD/BUILD2011/TOOL-930C

Portable Library Tools Release

Krzysztof Cwalina — Wed, 15 Jun 2011 17:49:44 GMT

We just released the official version of the Portable Library Tools. The set of tools and updates to .net platform allow you to create dlls that can be used in .NET Framework, Silverlight, Windows Phone, and XBOX projects. You can download the tools here and read more about them on MSDN.

MEF Primitives Explained

Krzysztof Cwalina — Tue, 09 Jun 2009 19:48:00 GMT

Daniel just wrote a really nice post explaining the basics of MEF primitives. I recommend this to all interested in the internals or in extending MEF.

Custom Programming Models for MEF (Provider Model Contrib)

Krzysztof Cwalina — Wed, 04 Mar 2009 01:12:00 GMT

The MEF composition engine operates on (composes) abstractions called ComposableParts. By default, parts are implemented as simple .NET classes annotated with MEF attributes (ExportAttribute and ImportAttribute). But, we envision that some parts will be implemented through variety of different mechanisms. For example, parts can be .NET types annotated with external files, DLR objects, XAML files, etc. We call such alternative means of specifying parts “custom programming models.”

In v1 of MEF, we focused on getting the default programming model super easy to use (most MEF users need to only understand a handful of types) and getting the ComposablePart abstractions right (making it possible to create custom programming models). We did not focus on making it easy to create custom programming models (quite advanced scenario).

Andreas stepped in and filled in that hole. He created a MEF contrib project which is a set of helper libraries that make it quite easy to create custom programming models. For all those who like to play around with internals of technologies like MEF, I recommend looking at the library.

MEF Preview #4 Released

Krzysztof Cwalina — Tue, 27 Jan 2009 19:53:00 GMT

We have just released a new update to MEF. I am super excited about this release as it represents something quite close to what we are going to ship in terms of public APIs. In the last milestone, we have done quite significant API cleanup, renamed many core types to what I think will be their final names, and finally we have done some namespace factoring work. Now, the primitives, host APIs, and parts’ APIs are all in separate namespaces.

PDC 2008 Talk: Framework Design Guidelines

Krzysztof Cwalina — Thu, 30 Oct 2008 19:00:00 GMT

Our PDC talk has been posted on Channel9. http://channel9.msdn.com/pdc2008/PC58/.

Here is the talk summary:

Learn about guidelines that have helped the Microsoft .NET Framework grow into the most popular developer framework Microsoft has ever created. After ten years of use, we have an enormous amount of real customer data about what makes great framework design. Whether you are building your own framework or just want to get the most out of the .NET Framework, this is a must-attend talk! Join Krzysztof Cwalina and Brad Abrams, authors of the Dr. Dobbs award winning "Framework Design Guidelines" book, and get a sneak peek at the content from the 2nd edition (first available at PDC2008).

Framework Design Guidelines Videos

Krzysztof Cwalina — Mon, 27 Oct 2008 20:00:00 GMT

Brad and I just did a couple of video interviews that are now accessible online.

In the first one, we are talking about our PDC presentation (for those at the PDC, it’s at 4pm today). You can get it at 10 Years of Framework Design Guidelines (video).

The second interview is about just released 2^nd edition of the Framework Design Guidelines book. You can get the video at Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries (video)

Enjoy!

MEF on CodePlex

Krzysztof Cwalina — Sat, 06 Sep 2008 00:00:00 GMT

We have just released an update to MEF. You can get it at http://www.codeplex.com/MEF

The changes are quite significant:

1. The preview ships with sources under a very permissive license (Ms-LPL).

2. We now support constructor injection. Feature that the community asked for.

3. We completely redesigned MEF’s extensibility points. The extensibility points are designed to support writing custom providers of composition data. For example, out of the box MEF requires composable parts to be attributed with attributes that provide metadata describing the composition. We got lots of feedback that this is not acceptable in many scenarios. The new extensibility points make it easier to extend MEF to externalize the metadata (to an XML file for example). Note, that the changes are just the first step toward the goal of making the extensibility easy and powerful. We will most probably keep making improvements in this space in the future, so feedback on the new extensibility points would be more then welcome.

4. We significantly cleaned up the container APIs. But as above, there is more clean up to come in the future.

Extensible Framework Design Studio Released

Krzysztof Cwalina — Sat, 30 Aug 2008 20:19:00 GMT

This summer we had a high school intern, Nick Moloney, who worked on incorporating MEF into FDS. The fruits of his labor are now on code gallery. You can download the extensible FDS here. Congratulations to Nick!

The current release has just a few extensibility points, but you should expect more in the future.

API Design Myth: Exceptions are for "Exceptional Errors"

Krzysztof Cwalina — Thu, 17 Jul 2008 23:09:00 GMT

I was updating FDG section on exceptions. I added one anntation that I thought I would post here as well:

KRZYSZTOF CWALINA

One of the biggest misconceptions about exceptions is that they are for “exceptional conditions.” The reality is that they are for communicating error conditions. From a framework design perspective, there is no such thing as an “exceptional condition”. Whether a condition is exceptional or not depends on the context of usage, --- but reusable libraries rarely know how they will be used. For example, OutOfMemoryException might be exceptional for a simple data entry application; it’s not so exceptional for applications doing their own memory management (e.g. SQL server). In other words, one man’s exceptional condition is another man’s chronic condition.

Nullable Usage Guidelines

Krzysztof Cwalina — Wed, 16 Jul 2008 23:47:00 GMT

These guidelines were just added as part of an update to the Framework Design Guidelines book (upcomming 2nd edition). Hope you find them useful.

Nullable<T> is a simple type added to the .NET Framework 2.0. The type was designed to be able to represent Value Types with “null” values.

Nullable<int> x = null;

Nullable<int> y = 5;

Console.WriteLine(x == null); // prints true

Console.WriteLine(y == null); // prints false

Note that C# provides special support for Nullable<T> in the form of language aliases for Nullable types, lifted operators, and the new coalescing operator.

int? x = null; //

long? d = x; // calls cast operator from Int32 to Int64

Console.WriteLine(d??10); // coalescing; prints 10 because d == null

þ CONSIDER using Nullable<T> to represent values that might not be present (i.e. optional values). For example, use it when returning a strongly typed record from a database with a property representing an optional table column.

ý Do NOT use Nullable<T> unless you would use a reference type in a similar manner, taking advantage of the fact that reference type values can be null.

For example, you would not use null to represent optional parameters.

// bad design

public class Foo {

public Foo(string name, int? id);

}

// good design

public class Foo {

public Foo(string name, int id);

public Foo(string name);

}

ý AVOID using Nullable<bool> to represent a general three-state value.

Nullable<bool> should only be used to represent truly optional Boolean values: true, false, and not available. If you simply want to represent three states (e.g. yes, no, cancel), consider using an enum.

ý AVOID using System.DBNull. Prefer Nullable<T> instead.

Nullable<T> is in general a better representation of optional database values. One thing to consider though it that while Nullable<T> gives you the ability to represent null values, you don’t get database null operational semantics. Specifically, you don’t get null propagation through operators and functions. If you deeply care about the propagation semantics, consider sticking with DBNull.

POCO Support for MEF

Krzysztof Cwalina — Mon, 07 Jul 2008 21:37:00 GMT

Jason, our technical evangelist, just posted a sample showing how MEF can compose plain old CLR objects.

MEF and System.AddIns

Krzysztof Cwalina — Fri, 13 Jun 2008 19:04:00 GMT

Several people asked about the relationship between MEF and the technology in System.AddIn namespace. The answer is that these two are independent and complementary features. MEF is a primarily a composition engine. System.AddIn is an add-in activation and isolation technology. MEF’s engine will be able to compose objects that are simple CLR object, COM and DCOM components (more precisely managed proxies to these components), remoting proxies, and finally System.AddIn add-ins.

The following is roughly how we see the basic “architecture” (conceptual diagram) of these technologies. As you can see on the diagram, the composition engine works on abstract representations of components currently called ComponentBinders. The composition engine is not concerned with how the parts are actually implemented or activated (COM, simple new operator, or System.AddIns activation). Its only concern is to inspect the binders for dependencies they need (imports) and objects they can give (exports), and provide “matchmaking” services for the binders (blue arrows on the diagram).

MEF CTP 1 Released

Krzysztof Cwalina — Thu, 05 Jun 2008 23:53:00 GMT

Several members of my team have already spilled the beans, but yes (!) we just released our first public preview of MEF. You can grab the bits from here and read a past post for a high level overview.

I am super excited about the release. It’s a very early preview and still lots of work remains, but the CTP is a significant milestone for us. Designing a general purpose extensibility framework is hard, and so we felt very strong about releasing such an early preview to the world to get early feedback from the community. Hopefully together we can create a set of APIs that scale to the variety of extensibility scenarios: from developers using DI and IoC to large applications with extensibility points and plug-ins.

In my previous post about MEF, several people asked about constructor injection and non-attribute based programming model. Constructor injection is not supported in this preview, but we did start working on the design of the composition engine that would allow it. The non-attribute based programming model (where connections are specified externally) is actually enabled, but not built-in. I will try to post a sample showing how to do it, but for those that want to experiment themselves: you need to implement a custom component binder. The built-in binder inspects types and looks for the attributes. You custom binder might want to read the same information (which type to inject where) in some external file.

Managed Extensibility Framework

Krzysztof Cwalina — Fri, 25 Apr 2008 19:45:00 GMT

Several months ago we formed what we call Application Framework Core team. The charter of the team is to play the same role in the application frameworks space (WinForms, ASP.NET, WPF, Silverlight) as the Base Class Libraries (BCL) team plays at the bottom of the platform stack.

The BCL team did a good job fulfilling the role of the team responsible for decreasing duplication and providing common abstractions for the low levels of the platform. Unfortunately, we did not have a similar team really focused on these sets of issues higher up on the stack. This resulted in some unfortunate duplication (like several data binding models for each of the application models, different dependency property system for WPF and WF) and lack of common abstractions (what undo APIs should my generic application plugin call?) for application model code. The Application Framework Core team is now in place to start addressing the problems.

One of the first concrete projects that we are working on and are ready to slowly talk about is what we call the Managed Extensibility Framework (MEF). We observed that there are more and more places in the .NET Framework itself and increasingly managed applications (like Visual Studio) where we want to provide, or already provide, hooks for 3^rd party extensions. Think about TraceListener plugins for the TraceSource APIs, pluggable rules for Visual Studio Code Analysis (and the standalone FxCop), etc. In the absence of a built-in extensibility framework (like MEF), our developers who want to enable such extensions often are forced to create custom mechanisms, thus duplication. We hope that MEF will both stop such duplication and encourage/enable more extensibility in the Framework and applications built on top of it.

We will blog more details about MEF in the upcoming months, but here are some early details (subject to changes, of course): MEF is a set of features referred in the academic community and in the industry as a Naming and Activation Service (returns an object given a “name”), Dependency Injection (DI) framework, and a Structural Type System (duck typing). These technologies (and other like System.AddIn) together are intended to enable the world of what we call Open and Dynamic Applications, i.e. make it easier and cheaper to build extensible applications and extensions.

The work we are doing builds on several existing Microsoft technologies (like the Unity framework) and with feedback from the DI community. The relationship with the Unity team is the regular relationship between the P&P group and the .NET Framework group where we trickle successful technologies and ideas from the P&P team into the .NET Framework after they have passed the test of time. We have done this with some features in the diagnostics, exceptions, and UI space in the past. The direct engagement with the DI community is also starting. We gave a talk on the technology at last week’s MVP Summit, and talked with Jeremy Miller (the owner of Structure Map) and Ayende Rahien (Rhino Mocks) . We got lots of great feedback from Jeremy and Ayende and I think their experience in the DI space and their feedback will be invaluable as the project evolves. Thanks guys! We are of course also looking forward to engaging others in the DI community.

And finally here is some code showing basic scenarios our framework supports:

Creating an Extension Point in an Application:

public class HelloWorld {

[Import] // import declares what a component needs

public OutputDevice Output;

public void SayIt() {

Output.WriteLine("Hello World");

}

// Extension Contract

public abstract class OutputDevice {

void WriteLine(string output)

}

1. Creating an Extension

[Export(typeof(OutputDevice))] // export declared what a component gives

public class CustomOutput : OutputDevice {

public void WriteLine(string output) {

Console.WriteLine(output);

}

2. Magic that makes composes (DIs) the application with the extensions.

var domain = new ComponentDomain();

var hello = new HelloWorld();

// of course this can be implicit

domain.AddComponent(hello);

domain.AddComponent(new CustomOutput());

domain.Bind(); // bind matches the needs to gives

hello.SayIt();

Expecting lots of questions, I will preemptively answer (J): we don’t yet know whether or when we will ship this. We do have working code and we are looking into releasing a preview/CTP of the technology. For now we would be very interested in high level feedback. What do you think hinders extensibility in frameworks and application? Where would you like the Framework to be more extensible? What DI framework features you need, like, want, and use on daily basis? i.e. is constructor injection required?

And lastly, we are hiring! :-)

Framework Design Guidelines Digest v2

Krzysztof Cwalina — Thu, 10 Apr 2008 00:19:00 GMT

Almost 4 years ago, I blogged about Framework Design Guidelines Digest. At that time, my blog engine did not support attaching files and I did not have a convenient online storage to put the document on, and so I asked people to email me if they want an offline copy.

Believe it or not, I still receive 1-2 emails a week with requests for the offline copy. Now that I have a convenient way to put the document online, and the fact that I wanted to make some small updates, I would like to repost the digest. The abstract is below and the full document can be downloaded here.

This document is a distillation and a simplification of the most basic guidelines described in detail in a book titled Framework Design Guidelines by Krzysztof Cwalina and Brad Abrams. Framework Design Guidelines were created in the early days of .NET Framework development. They started as a small set of naming and design conventions but have been enhanced, scrutinized, and refined to a point where they are generally considered the canonical way to design frameworks at Microsoft. They carry the experience and cumulative wisdom of thousands of developer hours over several versions of the .NET Framework.

Framework Design Studio Released

Krzysztof Cwalina — Fri, 04 Apr 2008 21:10:00 GMT

When I was coming back from Mix 2007, I was bored on the plane and so started to write a dev tool. What a geeky thing to do on a plane. :-)

The tool allows comparing two versions of an assembly to identify API differences: API additions and removals. Comparing versions of APIs comes very handy during API design process. Often you want to ensure that things did not get removed accidentally (which can cause incompatibilities), and as APIs grow, you want to review the addition without having to re-review APIs that were already reviewed. The tool, called Framework Design Studio (FDS) supports these scenarios.

Later on, I got lots of help from Hongping Lim (a developer on our team), and David Fowler (our 2007 summer intern). David ported the application to WPF, and Hongping basically took it from an early prototype stage to what it is today and made it possible to ship it externally.

Anyway, you can get the tool at the MSDN Code Gallery, the user guide is attached to this post, and lastly, here is the API diff output that the tool generates. Hope you find it useful.

Simulated Covariance for .NET Generics

Krzysztof Cwalina — Wed, 02 Apr 2008 18:00:00 GMT

I just wrote this pattern, but I am not sure if I should add it officially to the Framework Design Guidelines. It seems like a bit of a corner case scenario, though I do get questions about it from time to time. Anyway, let me know what you think.

Different constructed types don’t have a common root type. For example, there would not be a common representation of IEnumerable<string> and IEnumerable<object> if not for a pattern implemented by IEnumerable<T> called Simulated Covariance. This post describes the details of the pattern.

Generics is a very powerful type system feature added to the .NET Framework 2.0. It allows creation of so called parameterized types. For example, List<T> is such a type and it represents a list of objects of type T. The T is specified at the time when the instance of the list is created.

List<string> names = new List<string>();

names.Add(“John Smith”);

names.Add(“Mary Johnson”);

Such Generic data structures have many benefits over their non-Generic counterparts. But they also have some, sometimes surprising, limitations. For example, some users expect that a List<string> can be cast to List<object>, just as a String can be cast to Object. But unfortunately, the following code won’t even compile.

List<string> names = new List<string>();

List<object> objects = names; // this won’t compile

There is a very good reason for this limitation, and that is to allow for full strong typing. For example, if you could cast List<string> to a List<object> the following incorrect code would compile, but the program would fail at runtime.

static void Main(){

List<string> names = new List<string>();

// this of course does not compile, but if it did

// the whole program would compile, but would be incorrect as it

// attempts to add arbitrary objects to a list of strings.

AddObjects((List<object>)names);

string name = names[0]; // how could this work?

}

// this would (and does) compile just fine.

static void AddObjects(List<object> list){

list.Add(new object()); // it’s a list of strings, really. Should we throw?

list.Add(new Button());

}

Unfortunately this limitation can also be undesired in some scenarios. For example, there is nothing wrong with casting a List<string> to IEnumerable<object>, like in the following example.

List<string> names = new List<string>();

IEnumerable<object> objects = names; // this won’t compile

foreach(object obj in objects){

Console.WriteLine(obj.ToString());

}

In general, having a way to represent “any list” (or in general “any instance of this generic type”) is very useful.

// what type should ??? be?

static void PrintItems(??? anyList){

foreach(object obj in anyList){

Console.WriteLine(obj.ToString());

}

Unfortunately, unless List<T> implemented a pattern that will be described in a moment, the only common representation of all List<T> instances would be System.Object. But System.Object is too limiting and would not allow PrintItems method to enumerate items in the list.

The reason that casting to IEnumerable<object> is just fine, but casting to List<object> can cause all sorts of problems is that in case of IEnumerable<object>, the object appears only in the output position (the return type of GetEnumerator is IEnumerator<object>). In case of List<object>, the object represents both output and input types. For example, object is the type of the input to the Add method.

// T does not appear as input to any members or dependencies of this interface

public interface IEnumerable<T> {

IEnumerator<T> GetEnumerator();

}

public interface IEnumerator<T> {

T Current { get; }

bool MoveNext();

}

// T does appear as input to members of List<T>

public class List<T> {

public void Add(T item); // T is an input here

public T this[int index]{

get;

set; // T is actually an input here

}

In other words, we say that in IEnumerable<T>, the T is at covariant positions (outputs). In List<T>, the T is at covariant and contravariant (inputs) positions.

To solve the problem of not having a common type representing the root of all constructions of a generic type, you can implement what’s called the Simulated Covariance Pattern.

Given a generic type (class or interface) and its dependencies

public class Foo<T> {

public T Property1 { get; }

public T Property2 { set; }

public T Property3 { get; set; }

public void Method1(T arg1);

public T Method2();

public T Method3(T arg);

public Type1<T> GetMethod1();

public Type2<T> GetMethod2();

}

public class Type1<T> {

public T Property { get; }

}

public class Type2<T> {

public T Property { get; set; }

}

Create a new interface (Root Type) with all members containing Ts at contravariant positions removed. In addition, feel free to remove all members that might not make sense in the context of the trimmed down type.

public interface IFoo<T> {

T Property1 { get; }

T Property3 { get; } // setter removed

T Method2();

Type1<T> GetMethod1();

IType2<T> GetMethod2(); // note that the return type changed

}

public interface IType2<T> {

T Property { get; } // setter removed

}

The generic type should then implement the interface explicitly and “add back” the strongly typed members (using T instead of object) to its public API surface.

public class Foo<T> : IFoo<object> {

public T Property1 { get; }

public T Property2 { set; }

public T Property3 { get; set;}

public void Method1(T arg1);

public T Method2();

public T Method3(T arg);

public Type1<T> GetMethod1();

public Type2<T> GetMethod2();

object IFoo<object>.Property1 { get; }

object IFoo<object>.Property3 { get; }

object IFoo<object>.Method2() { return null; }

Type1<object> IFoo<object>.GetMethod1();

IType2<object> IFoo<object>.GetMethod2();

}

public class Type2<T> : IType2<object> {

public T Property { get; set; }

object IType2<object>.Property { get; }

}

Now, all constructed instantiation of Foo<T> have a common root type IFoo<object>.

var foos = new List<IFoo<object>>();

foos.Add(new Foo<int>());

foos.Add(new Foo<string>());

…

foreach(IFoo<object> foo in foos){

Console.WriteLine(foo.Property1);

Console.WriteLine(foo.GetMethod2().Property);

}

þ CONSIDER using the Simulated Covariance Pattern, if there is a need to have a representation for all instantiations of a generic type.

The pattern should not be used frivolously as it results in additional types in the library and can makes the existing types more complex.

þ DO ensure that the implementation of the root’s members is equivalent to the implementation of the corresponding generic type members.

There should not be an observable difference between calling a member on the root type and calling the corresponding member on the generic type. In many cases the members of the root are implemented by calling members on the generic type.

public class Foo<T> : IFoo<object> {

public T Property3 { get { ... } set { ... } }

object IFoo<object>.Property3 { get { return Property3; } }

…

}

þ CONSIDER using an abstract class instead of an interface to represent the root.

This might sometimes be a better option as interfaces are more difficult to evolve (see section X). On the other hand there are some problem with using abstract classes for the root. Abstract class members cannot be implemented explicitly and the subtypes need to use the new modifier. This makes it tricky to implement the root’s members by delegating to the generic type members.

þ CONSIDER using a non-generic root type, if such type is already available.

For example, List<T> implements IEnumerable for the purpose of simulating covariance.

Job Openings on the .NET Framework Core Team

Krzysztof Cwalina — Fri, 14 Mar 2008 22:49:00 GMT

We have been incubating ideas about building a simple extensibility framework for some time. Now, as plans for the next version of the .NET Framework crystallize a bit more, we decided to productize the project. As a result, we have opened a job position (and most probably will be opening more) on the .NET Framework team. If you are interested, please see details here and send me an email at “kcwalina at microsoft.com.”

So, what is this extensibility framework? Initially, it will be a low level core .NET Framework feature to make it easy for applications to expose extensibility points and consume extensions. Think about what for example FxCop has to do define rule contracts and load rule implemented by the community. These are the basics, and we can talk about the broader and longer term vision when you come to Redmond for an interview :-)

This is a technical Program Manager position in Redmond, WA, and it’s basically exactly the job I did when I joined Microsoft. Besides working on the Framework features, all Program Managers on the core team have opportunities to work on API design and architecture projects.

LINQ Design Guidelines

Krzysztof Cwalina — Thu, 13 Mar 2008 07:13:00 GMT

Mircea, a program manager on my team, has worked on development of design guidelines for LINQ related features. The guidelines were reviewed internally and are now available on Mitch’s blog. We might still iterate on them a bit, but quite soon I plan to incorporate them into Framework Design Guidelines manuscript, so if you have feedback, it’s time to send it our way! :-)

Thanks!

Video Recording of "Framework Engineering: Architecting, Designing, and Developing Reusable Libraries"

Krzysztof Cwalina — Tue, 08 Jan 2008 21:42:00 GMT

I just received a video recording of a talk I did at the last TechEd. You can find the abstract below, and the WMV file can be downloaded from here. Hope you find it useful.

[UPDATE: I attched the slides in xps format. The ppt file is 10x larger]

Framework Engineering: Architecting, Designing, and Developing Reusable Libraries

This session covers the main aspects of reusable library design: API design, architecture, and general framework engineering processes. Well-designed APIs are critical to the success of reusable libraries, but there are other aspects of framework development that are equally important, yet not widely covered in literature. Organizations creating reusable libraries often struggle with the process of managing dependencies, compatibility, and other design processes so critical to the success of modern frameworks. Come to this session and learn about how Microsoft creates its frameworks. The session is based on experiences from the development of the .NET Framework and Silverlight, and will cover processes Microsoft uses in the development of managed frameworks.

Framework Design Guidelines 2nd Edition

Krzysztof Cwalina — Fri, 04 Jan 2008 01:39:00 GMT

My blog was relatively silent for several weeks. First, I was traveling to Europe for the TechEd, then was busy at work, then the holiday break. It's time to go back to more regular posting.

I will start with an announcement (or at least a more formal and broader announcement): after my TechEd presentation, the first question I got from the audience was whether we are working on a new edition of the Framework Design Guidelines. The answer is "yes", which I am super excited about. Right before the conference, we signed formal documents with the publisher and started wortking on the book. It's going to cover the new features in the .NET Framework 3.0, 3.5, and new advances in languages (e.g. LINQ) that are relevant to Framework design. BTW, I would appreciate feedback on what specifically you would like to get covered or clarified.

We are shooting to have the book ready around the end of 2008, but the publisher already sent me a draft of the cover art:

What Do Swimmers Have to Say About Framework Design?

Krzysztof Cwalina — Fri, 05 Oct 2007 03:09:00 GMT

I am starting to feel pressure to finish up slides for my presentation at the upcoming TechEd in Barcelona. I will be talking about framework architecture and design. Here is the abstract I took from the conference’s site:

WIN304 Framework Engineering: Architecting, Designing, and Developing Reusable Libraries

I am super excited about the talk, which I want to make into a continuation to the API design pre-con I did with Brad Abrams at the last PDC (BTW, the same content is available here). The PDC talk was about designing the API surface, but there is so much more to framework design!

I am also excited coming back to the wonderful city of Barcelona. Last time I was there, believe it or not, I was on the Polish swimming team competing in the Olympics (see #13). I hope this trip will bring back some memories from the other and completely different “career” I had in the past.

FxCop Rule for Multi-Targeting

Krzysztof Cwalina — Wed, 03 Oct 2007 02:50:00 GMT

Two months ago, Scott blogged about the multi-targeting support in Visual Studio 2008. I worked on this feature in the planning phase (read “long time ago”), and so I am quite thrilled to see it finally in the hands of developers. Especially, that several years ago I remember our small working group sitting in a room and wondering whether such feature was even possible. The complexities of implementing it in a large project like the Visual Studio seemed quite daunting.

The thing that made implementing multi-targeting in one release possible was the concept of Red and Green bits. You can read about the concept here, here, and here, but quickly: red bits are Framework assemblies that existed in the .NET Framework 2.0 and were serviced in versions 3.0 and 3.5. Green bits are assemblies that were added either in the version 3.0 or 3.5. The servicing changes in Red bit APIs are limited (after all it is servicing) to a very small number of API additions and bug fixes.

We leveraged (and influenced) the decision to limit the number of changes to existing assemblies to drastically simplify the requirements for the multi-targeting system. That is, we made an assumption that the majority of differences between the Framework versions (targets) are on assembly boundaries.

But now I have to confess, there are some limitations in this design that we accepted when we made the original simplifying assumption. There is a very limited number of APIs being added to the Red assemblies and the multi-targeting system is currently not able to detect these. For example, if you set the target to the .NET Framework 2.0 and read the newly-added (albeit obscure) property GCSettings.LatencyMode the program will compile just fine but then fail to run on the .NET Framework 2.0 RTM. The reason is that the property was added to an existing (Red) class GCSettings, not to a new class in a new assembly. Despite that the number of such additional APIs in Red bits is very small (and that we recommend that you still test your programs on all targeted platforms), this can be quite annoying. And so feeling a bit responsible for this (and trying to promote FxCop J), I wrote an FxCop rule that can analyze IL of an assembly targeted at Framework 2.0 and warn you about all calls to members that are not present in 2.0 RTM.

Here is how it works: The test program below uses new LatencyMode enum and calls a new GcSettings.LatencyMode property. As I mentioned above, these APIs don’t exist in .NET Framework 2.0 RTM. Even if I built this project with the multi-targeting target set to Framework 2.0, the system would not complain about calling these APIs. But, as you can see in the error list, the FxCop analysis engine can deal even with this difficult to detect problem. You can think of the rule as a very smart (post) compiler-step.

A sample project with the rule is attached to this post. I provide it without any guarantees, as is, and in fact I am sure it has many bugs and problems. When I find time, I will work on it more to polish it a bit but I don't promise (i.e. treat it as a sample).

BTW, to install the rule, just build it and drop it to the FxCop rules directory. On my machine it is at C:\Program Files\Microsoft Visual Studio 9.0\Team Tools\Static Analysis Tools\FxCop\Rules. In addition you have to go to Project settings of the project you want to analyze and turn on FxCop analysis (the “Code Analysis” tab in the project properties). Lastly, you can either rebuild or right click on a project and choose “Run Code Analysis”. I hope it’s helpful.

China Trip

Krzysztof Cwalina — Tue, 02 Oct 2007 21:42:00 GMT

Sorry for not blogging for such a long time. First I was on a combined business/vacations trip to China and when I came back, I got involved in some intensive planning for the future releases of the platform. I will try to post something about software in the next couple of days.

The trip to China was great. First day I taught a class on API design at the Microsoft center in Beijing and then my wife and I stayed for several days doing sightseeing, drinking the best tea ever, and indulging ourselves in great food (complete photo documentary is here).