Subclassing

Suppose we have a cached collection of User objects, and we want to fetch a specific User and save it to the database.

User user = cache.Get(”John”);
if (user != null)
{
     user.Save();
}

If we subclass User with a class called MissingUser, and have our cache object return it when it can’t find a user, we can reduce our calling code to:

User user = cache.Get(”John”);
user.Save(); 

MissingUser.Save() overrides User.Save() and does nothing.

Side note: we could definitely go with checking cache.Contains(”John”), and acting on the result, but I think this is too much detail for this level of abstraction, and may be violating Tell, Don’t Ask.

Instantiation

Suppose we want to display a User’s profile. Our User class has a string called Name and a bitmap called Picture.

User user = profiles.Get(”Mark”);
if (user != null)
{
     this.Name = user.Name; // Binding is for the weak.
     this.Picture = user.Picture;
}

When a User is not found in the profiles repository, we could make it return an instance of the regular User class, where User.Name = “Not Found”, and Picture is something like

This way, we can just write:

User user = profiles.Get(”Mark”);
this.Name = user.Name;
this.Picture = user.Picture;

and a profile will always be displayed.

Conditioning on Instantiation

What if we wanted to check if a User exists in a managers repository, and only if it is not found, fetch it from a clerks repository? One might be tempted to write something like:

User user = managers.Get(”Ahmed”);
if (user != null)
{
     // Ahmed is a manager.
     Display(user);
}
else
{
     // Ahmed must be a clerk.
     user = clerks.Get(”Ahmed”);
     Display(user);
}

In the previous examples, we avoided the conditional (null check) by using Special Case. If you look at the requirement for this example, you’ll see that the conditional is built into it, and there is no way to get around it.

But if we use the same technique we used in the second example, we could create an instance of User, that has a boolean property called Exists, which will be populated according to the result. This way, we could express our condition much better:

User user = managers.Get(”Ahmed”);
if (user.Exists)
{
     // Ahmed is a manager.
     Display(user);
}
else
{
     // Ahmed must be a clerk.
     user = clerks.Get(”Ahmed”);
     Display(user);
}

No code saved here, but our intention is much clearer this way.

What the hell is a “if (user != null)”? English, people.

public IEnumerable<Picture> GetAllPictures()
{
  if ( .. there are pictures .. )
  {
    return pictures;
  }
  else
  {
    return null;
  }
}

Oh boy, users of this method would have to check for nulls every time before they operate on it: (if they don’t they might get a NullReferenceException, which s-uhhh-cks)

var pictures = GetAllPictures();
if (pictures != null)
{
  foreach (var picture in pictures)
  {
    …
  }
}

Isn’t that null check a big distraction from the actual logic? If you use a Special Case for that enumerable and return Enumerable<Picture>.Empty(), the calling code could be reduced to:

var pictures = GetAllPictures();
foreach (var picture in pictures)
{
  …
}

Much better, no?

When you get assigned to implement feature X, unit tests are just another part of that assignment. Just like planning, compiling, banging your head on the keyboard or writing documentation.

Sure, I get it, you want to show that you are very trendy and professional, especially since the project manager has asked everyone to unit test. But if you want to be a real professional, just silently work on unit tests and say “I’m working on feature X”.

And write those unit tests before code. And don’t drink water from a puddle.

For example, I am currently testing a custom IList<T> implementation, and in a specific test case, I want to make sure a specific entry exists instead of another. Before compound constraints, I would have written these 2 asserts:

Assert.That(this.subject, Has.Member(”rauchy”));
Assert.That(this.subject, Has.No.Member(”Omer”));

My problem with this code is that these two asserts represent a single fact - I want to make sure that rauchy makes it to the list, and not Omer. One might interpert them as two independent facts. With compound constraints, I can just write:

Assert.That(this.subject, Has.Member(”rauchy”) & Has.No.Member(”Omer”));

This way, you cannot think of this as two independent facts. Also, this helps follow the one-assert-per-test rule.

I’ve seen dozens of holy wars regarding the subject of naming conventions - when a project starts, when a new team member comes along, when the team leader is replaced etc.

I used to think that a project should have a single naming convention, and everyone should follow it. Now, I’m not so sure any more. I mean, what is really so important about naming conventions? What makes a project with a unified naming convention better than a project without one?

Unity

The first argument for naming conventions is always unity. You want all your data members to look the same.

But, think of it, what is really that important about unity? What business value do you get from it? Does it cut down development time? Does it improve performance?

IMO, if one developer wants his field to be called “_identifier”, another wants “m_identifier” and the other wants “nIdentifier”, just let them! No one ever died from Hungarian notation or a “m_” prefix, I believe.

Readability

For those who still believe in Hungarian notation (or any of its siblings), readability seems to be a great argument for naming conventions.

However, Hungarian notation might have been a good argument a decade ago. Today, all IDE’s provide great intellisense, and one could determine the type of a member in a second by hovering on it.

Scope

Determining the scope of a variable (method or class) is important, but can also be easily discovered by intellisense.

Focus on What’s Important

I’m not trying to say you shouldn’t have a naming convention in your project. I’m just trying to say, don’t let it bother you so much.

Set up a naming convention at the beginning of the project, have your team members agree on it, but don’t hunt down any exception and have it fixed.

Write a unit test or get a cup of coffee instead.

Do you think naming conventions are important? Where would you draw the line?

I hope to learn some stuff I just never get around to, such as:

• Domain Driven Design,
• Behavior Driven Development,
• Domain Specific Languages.

I don’t think I’ll be able to share any knowledge, since I’m positive that I will be stunned by the high-level knowledge of the people there.

So I’m off to stare and drool. See you there!

I did, however, try to keep up and see what’s the fuss about extension methods, but I never got it. I mean, this is anti-encapsulation at it best - break into any type, do whatever you feel like. Total chaos.

So I gave it some time. I didn’t force it into any of my projects until the time was right. Then I finally got it - extension methods are ideal for little pieces of code which you need, but creating a utility class for them feels wrong.

For example, I was implementing a new feature for Regionerate a couple of days ago in which I had to sort a list, split it into distinct values and recursively sort it again.

Its a reflection-based sort and it has quite a bit of logic in it, so it had a class & unit tests just for it. I had to take care of the splitting thingy, but it felt wrong to add it as a method in the sort class, as it operates on lists. It really feels like a method that should run on IList<T>.

Subclassing List<T> for the job feels wrong - c’mon, how would you pitch such a class? “It’s a list that you can split!”. Unpersuasive.

That’s how I got it: If IList<T> was built especially for Regionerate, it would have had a reflection-based Split function, but since its not, I should implement it as an extension method.

Took me 2 minutes and works like a charm.

   1:  public static IDictionary<object, IList<T>> Slice<T>(

   2:          this IList<T> list, PropertyInfo propertyInfo)

   3:  {

   4:      IDictionary<object, IList<T>> slices = 

   5:          new Dictionary<object, IList<T>>();

   6:      foreach (T t in list)

   7:      {

   8:          // Get the value of propertyInfo.

   9:          object value = propertyInfo.GetValue(t, null);

  10:   

  11:          // Add it to slices.

  12:          if (slices.Keys.Contains(value))

  13:          {

  14:              // slices already has a slice for this value.

  15:              slices[value].Add(t);

  16:          }

  17:          else

  18:          {

  19:              // there is no slice for this value 

  20:              // inside slices, create a new slice.

  21:              IList<T> newSlice = new List<T>();

  22:              newSlice.Add(t);

  23:              slices.Add(value, newSlice);

  24:          }

  25:      }

  26:   

  27:      return slices;

  28:  }

A fully documented, well-aligned version of this extension method is freely available here.

Note: yes, this post should have been a tweet, but I’m Twitterless.

Krzysztof Cwalina

I’ve read Framework Design Guidelines a couple of years back and learned a whole lot from it. It definitely makes it to my top 5.

However, I’ve had problems convincing my staff members to read it, as it contains~400 pages of design tips, which are quite hard to read in succession.

The Framework Design Guidelines Digest narrows the basics down to 9 pages. I recommend everyone to download and read it every once in a while.

Quoting Krzysztof:

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.

Get it here.

We split to several teams - development, marketing, user experience etc’. Over at the development team we split to front and back end teams.

I wrote a YouTube adapter yesterday for uploading and displaying YouTube videos, hope to post about it later on.

Looks like I’ll be doing some NHibernate today.

Can’t really write too much as I’m late, again, for day III, but:

1. Some pretty great guys out there, its always nice to reach outside your circle of colleagues.
2. People are smart.
3. People are stupid.

The only important things I’ve learned from talking to a nice gentleman from marketing is that if you plan to release a killer app in a domain which has already been harvested, your chance to succeed aren’t that big. Most successful application we see today recognized an un-harvested domain and conquered it.

Keep following on Twitter, I’m off!