Tag: list

No More Collection Objects

Posted by bsstahl on 2015-10-27 and Filed Under: development 

I don't create collection objects anymore.

I know, I know. I was they guy always preaching that every entity that was being collected had to have its own collection object. It was the right thing at the time; if you needed to take an action on an enumeration or list of objects, those actions needed to be done within a strongly-typed collection object to maintain encapsulation. Even if all that was happening was that an inherited List<T> function was being called, that functionality needed to be called on the TCollection object because, if it wasn't, it was likely that the next time logic needed to be performed on the collection, there wouldn't be a place to put it. Collection logic would end up being spread-out around your code rather than encapsulated in the collection. It was also possible that the implementation might change and need to be updated everywhere, instead of in one place.

Today however, that has all changed. Extension methods now allow us, at any time, to add functionality to ICollection<T>, IList<T>, IEnumerable<T> or any other interface or class. We can attach our list or enumeration based actions directly to the list or enumeration class, and do so at any time, since the methods appear the same to the developer as methods directly on the collection type. Thus, the "no place to put it" fear no longer exists. I've even started using this technique for my factory methods to make it clear that what I am creating is, in fact, an IEnumerable<T>, as in this example.

var stations = (null as IEnumerable<Station>).Create();
var localStations = stations.GetNearby(currentLocation);

In this example, both the Create and GetNearby methods are extension methods found in a static class called StationExtensions.

So, the big advantage here is that these methods can be added anytime, meaning we don't need to create an object that we MAY need in the future. This is better adherence to the YAGNI principle so it is a better pattern to follow. But what about disadvantages? Does it hurt us in any way to perform our collection actions this way? I'm not comfortable answering that question with an absolute "no" yet because I don't think I've been using this technique long enough to have covered enough ground with it, but I can certainly say that I haven't found any disadvantages yet. It seems like these extension methods are basically perfect for this type of activity. These methods do everything that the methods of a collection object do, can (and should) be put in a separate module to keep the code together, can be navigated to by Visual Studio in the same way as other methods, and have the same access (private, internal, public) restrictions that collection objects have. About the only thing I can say that is not 100% positive about using these techniques is that the (null as IEnumerable<T>) syntax to create a local variable instance to call the class factory from is not quite as elegant as I'd like it to be.

So you tell me, do you still create collection objects? Have you found any reason why using extension methods in this way is not as good as putting those methods into a strongly-typed collection? Sound off in the Fediverse @bsstahl@cognitiveinheritance.com and let's talk about it.

Tags: class coding-practices csharp development encapsulation entity generics inheritance list visual studio yagni 

Encapsulation and Generic Lists

Posted by bsstahl on 2007-09-16 and Filed Under: development 

It has often been said that each new language feature gives programmers more rope with which to hang themselves. Unfortunately, what it really seems like is that each feature gives other programmers more rope with which to hang me, or you, or whomever the next poor schmuck is who has to deal with their code. Back in the relatively early days of .NET 2.0, I wrote about some concerns I had with Generics. It has turned out that Generics are everything I could have hoped for in a language feature, and everything I feared.

Generics are an outstanding way of dealing with a number of issues in a very elegant, but also type-safe way. Among many things, this includes collections. I see no reason why there should be any new collections created that are not based on Generics and it is my understanding that System.Collections.CollectionBase (the non-Generic base collection class) is to be deprecated sometime in the near future. However, as I feared over a year ago, there are many that miss the point somewhat and expose List<t> on their interfaces. The Generic List object is a very powerful and easy to use collection, but it is not extensible. If you write code that exposes List<t>, you are effectively passing a strongly-typed array-list. Doing this breaks encapsulation because any code we write against that list, has to be repeated everywhere we want to perform that operation.

For example, suppose we have a calendar object that exposes a list of events that we want to reserve. We often see this code:

  List<CalendarEvent> calendarEvents = Calendar.Events;  
  for each (CalendarEvent evt in calendarEvents)  
      evt.Reserve();

rather than the far preferable:

  CalendarEventsCollection calendarEvents = Calendar.Events;  
  calendarEvents.Reserve();

where the CalendarEventsCollection object contains:

  public void Reserve()  
   {  
       for each (CalendarEvent evt in this)  
           evt.Reserve();   
   }

or even better:

  Calendar.ReserveEvents();

where the Calendar object contains:

  private CalendarEventsCollection _calendarEvents;  
  public CalendarEventsCollection Events  
    { return _calendarEvents; }  
  
   public void ReserveEvents()  
   {  
       this.Events.Reserve();  
   }

The latter being preferable because all of the functionality we want to expose is completely encapsulated in the appropriate object and doesn't have to be repeated wherever it is needed. Of course, we can't do this if we are lobbing around List instead of collection objects that derive from System.Collections.ObjectModel.Collection.

While the improper use of List may not be exactly the "House of Sticks" that I feared in early 2006, it is an item where proper use is not necessarily obvious and which has been misunderstood by many very good programmers.  Please, encourage all developers to practice proper encapsulation by deriving collection classes from one of the Generic collection implementations.

Tags: encapsulation generics list