Another two C# idioms

This post is part of the series "C# idioms"

1. Two C# idioms
2. Another two C# idioms This post
3. Two C# idioms: On Dictionaries
4. Two C# idioms: On defaults and switch

In this part of the C# idioms series, we have one idiom to organize versions of commands, events or view models. And another idiom, on coditionals inside switch statements.

Separate versions of commands and events using namespaces and static classes

Sometimes you need to support versions of your objects to add new properties or remove old ones. Think of, commands and queries when working with Command Query Responsibility Segregation (CQRS), or request and response view models in your API projects.

One alternative to organize classes by version is to encode the version number in the class name itself. For example, DoSomethingCommandV2.

For better organization, separate your commands and queries inside a namespace named with the version number.

namespace Commands.V2
{
  public class DoSomethingCommand
  {
  }
}

But, someone could use one version instead of the other by mistake. Imagine someone writing the class name and using Ctrl + . in Visual Studio to resolve the using statement blindly.

Another option to group classes by vesion is to wrap your commands and queries inside an static, partial class named after the version number.

namespace Commands
{
    public static partial class V2
    {
        public class DoSomethingCommand
        {
        }
    }
}

When using static classes to separate classes by version, you will use the version number up front. Something like, V2.DoSomethingCommand. This time, it’s obvious which version is used.

But, if you use a partial classes and you keep your commands and events in different projects, you will end up with a name conflict. There will be two V2 classes in different projects. Then you would need to use an extern alias to differentiate between the two.

Finally, you can take the best of both worlds, namespaces and wrapper static classes.

namespace Commands.V2
{
    public static partial class V2
    {
        public class DoSomethingCommand
        {
        }
    }
}

Conditional cases in switch statements

When working with switch statements, you can use a when clause instead of an if/else in your case expressions.

Before, we used if inside switches

switch (myVar)
{
  case aCase:
    if (someCondition)
    {
      DoX();
    }
    else
    {
      DoY();
    }
    break;
    
    // other cases...
}

After, we use when in our case expressions

switch (myVar)
{
  case aCase when someCondition:
      DoX();
      break;
  
  case aCase:
      DoY();
      break;
      
  // other cases...
}

Order is important when replacing if/else inside cases with when clauses. The case/when should be higher than the corresponding case without when.

Voilà! Keep your command, queries and view models organized by versions with namespaces, static classes or both. Use when in switch statements.

Don’t miss the previous C# idioms to refactor conditionals and the next two C# idioms to get rid of exception when working with dictionaries.

Happy C# time!