In my current F# project, I’ve employed a very simple library to support basic contract checking. It’s not fantastically clever, but I thought I’d post it here in case others find it useful.

To use the library, pipe values into the various functions of the “Is” module. For example…

If either of the two preconditions highlighted above fail, a ContractFailureException will be thrown.

The full module is below. Again, the following code isn’t exactly rocket science, but I’ve found it dead useful, and you might, too.

Enjoy!

The last several weeks have been pretty hectic for me. First, Visual Studio 2010 and .NET Framework 4 shipped. Of course, only those living in caves and under rocks missed that bit of news. However, that event forced me to leave my own cave and make a few public appearances.

• April 12-15 - DevConnections, Las Vegas
  
  One thing that I love about the Bellagio is how they go out of their way to make me comfortable by naming their convention center rooms after the Teenage Mutant Ninja Turtles. Let’s see, there’s Michelangelo… Raphael… Donatello… Huh? What do you mean the rooms were named after Renaissance painters?
  
  
• April 26 - .NET Rocks Road Trip, Houston
  
  Hanging out with Carl and Richard is always a blast. In the past, I’ve been left with stories that I can’t really share in mixed company. This time they turned on the microphones and pressed “record.”
  
  
• June 7-10 – Tech Ed 2010, New Orleans
  
  I’ll be there. Who else is coming?

A few weeks ago, some of my colleagues and I were discussing the idiosyncrasies of various programming languages (as we often find ourselves doing—we’re kind of geeky that way), when one of us pointed out that the following code is completely valid C++0x syntax:

The “operator soup”¹ above defines a C++ lambda expression (denoted by the square brackets) which declares no parameters (the first empty parentheses) or body (the empty curly braces) and is immediately invoked (the final parentheses). Conceptually, this is a nop—an empty lambda that is immediately invoked.

We found ourselves fascinated by this idea of a do-nothing lambda, and went ahead to define the same thing in our respective languages. Our first attempt was C#.

While the code above looks quite pretty, it’s not exactly legal. In C#, lambdas must always have an explicit delegate type, so an ugly type-cast is required in order to compile:

Sigh, so close, yet so dissatisfying!

The stronger notion of type inference in F# allows for much more succinctness.²

However, my favorite version is written in Visual Basic 10.

What it lacks in succinctness,³ it makes up for with human-readable clarity.

How do you write a do-nothing lambda in your language?

¹One could also declare the square brackets with either an = or & operator inside to define how variables that are declared in the same scope as the lambda are captured within the lambda function’s closure. It’s amazing how much one can do without typing a single identifier character!

²Note that the F# example contains a subtle difference from the others in that it returns a value of type Unit. This implies that the entire F# expression could be passed as an argument to another function, but that is not true of the other examples.

³Though it’s the same size as the C# version when unnecessary whitespace characters are removed.

Now that Visual Studio 2010 Beta 2 is finally out the door, I’ve had a bit more time to spend coding on some of my personal projects. Yesterday, I happened upon a cool trick while using the new Generate from Usage feature. It was so helpful to me that I thought others might benefit, so I’m sharing it here.

The Anonymous Type Problem

When you need to project some data from a LINQ expression, anonymous types can be enormously convenient.

Because anonymous types are… well… anonymous, they don’t have names that can be expressed in code. This is problematic if you want to expose an anonymous type as the return type of a function. I have run into this problem many times. When refactoring code, it’s easy to get into a situation like the one below.

So, how can you get around this problem? Well, there a few possibilities.

1. You could replace ??? with object and use reflection to get at the properties. (Yuck!)
2. You could make the function generic and add a parameter to “mumble” the anonymous type.¹ (Awkward!)
3. Assuming C# 4.0, you could replace ??? with dynamic.² (No compiler errors!)

Because none of these solutions is particularly savory, most of us are forced to create a new named type to replace the anonymous type. Thankfully, there are some fantastic third-party refactoring tools out there that can automate this tedious process, but if you don’t use one of these tools you’re stuck writing the code by hand.

Actually, no, that’s not quite true.

Generate from Usage to The Rescue!

In Visual Studio 2010, the new Generate from Usage feature makes the task of coding up new classes a snap! Just type a new name for the anonymous type in the editor, making the code look like a type constructor followed by an object initializer. Then, press Ctrl+. to expand the smart tag that immediately appears and choose the first suggestion to generate a new class.

Next, expand each smart tag in the object initializer to generate each property.

When you’re finished, you should have a brand new class containing each property, declared as auto-implemented properties. Cool!

For Visual Basic coders, Generate from Usage is even easier. Let’s start with the same LINQ expression in VB. (Notice the lack of the “_” line continuation characters. Hooray for VB10 implicit line continuation!)

Just like before, type the name of the new type that you wish to generate and press Ctrl+. to expand the smart tag. After choosing the first suggestion from the smart tag, you’re finished. The VB Generate Class feature will drill into the object initializer and generate all of the necessary properties at the same time that the class is generated.

Wrapping Up

Of course, this technique is not without flaws.

• The resulting type is not immutable like the anonymous type that you’re replacing. To address this, you can easily modify the generated properties to be read-only.
• The new type does not have the same structural equality semantics that anonymous types have. In practice, I’ve rarely run into an bug caused by anonymous type structural equality, but if this is a concern for you, use one of the excellent third-party tools that account for these differences.

¹See Wes Dyer's excellent article for an example of this clever trick.
²Check out Bill Wagner's post for details.

The other day, I caught a quick snapshot of Bethany playing with her favorite new toy:

A special thanks to my friend Joseph Hill for providing her favorite monkey!

Last October, DevExpress released a massively powerful FREE tool specifically for C# developers called CodeRush Xpress. Today, in partnership with Microsoft, DevExpress has outdone themselves with a brand new version of CodeRush Xpress containing full support for both C# and Visual Basic. This release merges CodeRush Xpress with Refactor! for Visual Basic, creating one giant über-tool with an amazing features:

• Duplicate Line
• Highlight All References
• Increase or Reduce Selection
• Smart Clipboard Operations
• Generate from Using (TDD)
• Quick Navigation Window
• Quick File Navigation
• 60+ Refactorings!

Get it while it’s hot! You can download your FREE copy of CodeRush Xpress for Visual Studio 2008 from http://devexpress.com/crx.

I’m back again with another post in my Yet Another Project Euler Series. As a reminder, my approach to these problems is to try to find the most beautiful solution that I can using F#. While performance is an important, I’m looking for the most elegant solutions that I can find.

Project Euler problem ten is another dealing prime numbers.

The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

Find the sum of all the primes below two million.

As you can guess, there’s not too much to this problem. In fact, we’ll declare just one simple supporting function.

Using the above function and our existing prime number generator, our solution is short and simple.

I feel a little guilty that this post is so short, but that’s the benefit of spending two whole blog posts working out a prime number generator for problem seven.