John Reese

4 posts

Keep Your Collection Setters Private

When exposing properties of a class, you may find yourself immediately exposing a public getter and a public setter. This is a very common approach, especially in anemic models. However, this approach can be problematic when applied to collections. Allowing consumers of your collection to freely modify the entire collection is very destructive. In this post, I will go over two scenarios in which a public setter on your collection can get you into trouble.

You cannot iterate over a null collection

Lets compare two approaches to empty a collection. One approach that we could take is to call the .Clear() method like so:


Another approach, assuming we had a public setter, could be done by setting the collection to null:

myCollection = null;  

This is the first problem area for allowing public setters on your collections. By allowing your consumers to directly modify the collection, it's no longer possible to control how they will interact with your collection. Setting the entire collection to null for example, can potentially cause problems later in your programs life cycle.

Iterating over your collection is one of these pain points. The following code will behave differently if the collection is set to null, or if it is simply empty.

for(var item in collection)  
    // do stuff with collection items

If the collection was set to null, you will run into a lovely NullReferenceException, like the one below.

An unhandled exception of type 'System.NullReferenceException' occurred in YourProgramHere.exe

This is because all collections expose a GetEnumerator() method, which foreach leverages to iterate over your collection. If the collection is null, its GetEnumerator() method cannot be called. However, if the collection was simply empty via .Clear(), the run time error would not occur.

Events will not be triggered

Another problem that can arise is that it be very hard, if not impossible, to know when your collection has changed. Consider the following MyCollection class.

public class MyCollection  
    public ObservableCollection<int> Numbers { get; set; }

    public MyCollection()
        Numbers = new ObservableCollection<int>();
        Numbers.CollectionChanged += collectionChanged;

    private void collectionChanged(object sender, NotifyCollectionChangedEventArgs args)
        Console.WriteLine("Hey! Listen!");

This class defines a collection that will output some text when the collection changes. Now while this example only shows one collection, it could be entirely possible that this collection has many subscribers that wish to be notified when its contents change.

Using this collection, the only time the collectionChanged event will fire is when you leverage its .Add(), .Remove(), etc methods. Setting the collection to null will indeed empty the collection, but its subscribers will be unaware of anything that has happened.

In summary, when you expose a public setter on a collection, you are exposing much more behavior than you need to. It gives a lot of unnecessary control to your consumers, which could potentially put your collection into an undesirable state.

Prefer readonly to const

I was recently reading Effective C# by Bill Wagnar. In the book, the author makes the statement that we should prefer readonly to constants. I wasn't immediately able to piece together why we should, I mean, what's even the difference between the two? To answer this, let's first discuss how they're the same.

Both are static

Now obviously static readonly is static because it is decorated by the static keyword. One thing you may have overlooked however though, is that the const keyword is implicitly declared as static.

Static, put simply, means that whatever member it is decorating, belongs to the class itself rather than the object. The static member must be referenced by type and not by an instance. For example, the following code would not compile:

public class TheClass  
    public static void TotallyStaticMethod() { ... }
var someClass = new TheClass();  
someClass.TotallyStaticMethod(); // cannot be accessed with an instance reference;  

The above would generate a compiler error, specifically: Member 'TheClass.TotallyStaticMethod()' cannot be accessed with an instance reference; qualify it with a type name instead.

Both are immutable

Once declared readonly or const, the value cannot change. Now, there is a slight difference as to when the values become truly immutable. The value of a const must be initialized when it is declared. No sooner (though that'd be impressive) and no later.

On the other hand, readonly may be initialized during its declaration or in the constructor of the class that it was declared. This is useful for facilitating dependency injection through the constructor or even configuration values.

The biggest difference between the two?

Const is evaluated at compile time

What does this mean exactly? When you set the value of a constant, the compiler will actually take your variable assignment and bake it directly into the IL.

To see this in action, let's say we have the following code snippet.

namespace AnotherAssembly  
    public class Library
        public static readonly string ReadOnlyValue = "first readonly";
        public const string ConstValue = "first const"; 

If you were to compile the above code, reference the DLL in another project, and inspect the DLL with ILSPY (or your disassembler of choice) you would see the following output:

This clearly shows that our readonly variable is a reference type, referencing the ReadOnlyValue in the Library class which lives in AnotherAssembly. On the other hand, the const variable is being directly loaded with the value "first const".

This means that if you were to change the value of a const in an assembly, the assemblies that depend on that const will have the old value until they are rebuilt. This could cause a lot of headaches down the road, which is why it's always best to reserve const for values that you know will never change.

So while it is true that const will be slightly more performant than readonly, it's going to be a negligible amount. Always keep in mind that premature optimization is the root of all evil!


  1. const is evaluated at compile time, readonly is evaluated at runtime.
  2. Prefer const for values that you know will never change, for any reason.
  3. When in doubt, use readonly (the performance gain is negligible).

IIS Debugging Roulette

It's a typical day in the office. You've spent your day writing top notch unit tests and elegant code. You sit back, marvel at what you have accomplished and decide, being that good developer that you are, that maybe you should do some functional testing.

You navigate to the Debug pane, click your trusty "Attach to Process" and this familiar window pops up:

"Here we go again" you say to yourself, dreading what is to come next. You click on the first w3wp.exe process and attach. Nope.. doesn't look like that worked. You repeat this until you finally find the correct process to attach to so you can test your code. You hate having to do this every time you want to debug, but you accept it as a necessary evil of debugging an IIS process. It's just how it has to be done, right?

IIS Manager to the Rescue

You may be relieved to hear that this isn't how it has to be, there is hope! If you navigate your IIS Manager, you should see an option called Worker Processes underneath the IIS section.

After choosing this option, you will be presented with the Worker Process feature, which describes all of the w3wp.exe processes in greater detail than the debugger window. It is here that you can confidently link the application pool that you're trying to attach to with the correct process identifier. No more gambling!

Design Patterns are Solutions

I believe there comes a point in every budding software developers career, when they will decide that they should learn design patterns. After all, there is more to developing than copying and pasting code from stack overflow, right? They want to be able to engineer their own solutions.

However, the majority all seem to fall into a similar trap. They read book after book. Design Patterns Explained, Head First Design Patterns, and lets not forget what is considered the holy grail of design patterns, the Gang of Four.

They may then move onto routinely performing katas, such as the the Greed Kata to fully memorize, and perfect their Strategy Pattern implementation. Blissfully awaiting the time where they can actually utilize all of the knowledge they have gained.

Unfortunately, the developer will end up trying to fit the [insert design pattern here] design pattern into every problem, where it probably does not belong. It's a shiny new tool, and they just want to use it everywhere. This is a textbook case of starting with a solution, and trying to find a problem. Which should sound pretty backwards!

You could think of reading about design patterns as reading the answer key for a test. The answer key is going to give specific questions with specific answers. You will probably do really well on that test, but you will leave more than likely not knowing why those were the answers. After all, you didn't put any work into actually solving the problem. You saw a pattern, you knew the answer, and just implemented it without a second thought. What happens on the next test that doesn't include an answer key, but the context is relatively the same?

Design patterns are solutions. To appreciate a solution, you must first suffer from the problem. The issue with diving into patterns head first is that you will never truly understand why the solution exists in the first place. The importance of actually experiencing the pains first hand are almost completely ignored.

The point that I want to make most clear is that you should not try to find solutions to problems that you don't have.

Now, I'm obviously not saying that reading about design patterns is completely taboo. There are a lot of things that can be learned from reading. When learning design patterns however, I believe that the best way is to simply write code and make mistakes.

Go ahead and copy and paste your switch statement throughout your code base, what does it really matter? You'll soon find out when you want to introduce a new case in your statement.