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Archive Monthly Archives: September 2017

Avoid The Class Hierarchy Jungle: Favor Composition Over Inheritance

Have you ever worked on an application with a jungle-like class inheritance hierarchy? Everything in the app inherits from two layers of classes and it’s impossible to follow a single line of functionality. You get code reuse, but at the cost of incomprehensible spaghetti code. I, for one, find that price too steep. In this post, we’re going to learn how to build code that’s easy to reuse, easy to test, and most important, easy to read.

Composition > Inheritance

We have many design patterns in object oriented programming. One the most useful ones is the composite reuse principle (aka. composition over inheritance). This term sounds a little opaque, but it’s not hard to understand. It means that you should design your classes as a series of loosely coupled components instead of using a multilayered class hierarchy for code reuse.

Here’s an example:

Practically speaking, this means breaking down inheritance hierarchies into plug-able services. Then you can inject those services using your favorite dependency injection framework.

Why Bother?

While using composition may seem more complicated, there are several advantages.

  1. It’s far easier to reason about the code. If you divide up your functionality into small components, each component is simple. You’re dividing up the complexity of the application into manageable chunks. When you’re using complex inheritance, it’s difficult to figure out what block of code is executing. This is especially true once you start selectively overriding methods.
  2. It’s much easier to reuse a single component than to glue a class onto a hierarchy.
  3. It’s easy to unit test loosely coupled components. Building the appropriate mocks to test a complex class is painful. Mocking a few interfaces is much easier.

Spotting Refactoring Opportunities

There are a few potential anti patterns to keep an eye out for. 
“Base<thing>” classes. Especially base controllers (MVC), base pages (on Web Forms), and other base classes for classes that process data. Base classes for data storage objects are usually OK. ( ex: An Administrator that inherits from a Person class.) Using inheritance for processes is a bad idea. 
More than two layers of inheritance. It’s hard to imagine anything that needs more than two layers of inheritance.
Ginormous “God” classes that span 1000’s of lines. While not strictly related to using composition over inheritance, this goes against the idea of building a suite of simple components. Large classes are difficult to read and to test. Flattening a class hierarchy into a “God” class is not an improvement. 
Base classes with only one class that inherits from them. The base class here is superfluous. Feel free to get rid of it. 



If you’re using class hierarchy for code reuse, ditch that approach and favor composition instead. Your code base will thank you for it.

Further Reading




Cmder is the Cadillac of Windows Consoles

Like fashion, computing works in cycles. Things that were once looked at as passe come back with retro vengeance. For .NET development, the console is back. Consoles combined with lightweight editors like Visual Studio Code are becoming increasingly popular. Call me a hipster, but I’m all for this change. I hate waiting around for my editor and I never have to do that in a console or Visual Studio Code.

Unfortunately, if you’re living in the world of Windows, the default command line options are lacking. Not only are CMD and Powershell ugly, they lack basic usability features found in Linux and OSX. There is a better way. Cmder is a Windows console emulator that bundles several command line tools together into one fantastic package. It’s the Cadillac of Windows consoles.

Here’s what it looks like:

Cmder has a nice tabbed interface. You can run multiple consoles without having to deal with a bunch of windows. It also supports several different types of consoles including: CMD (enhanced with Clink), Powershell, and Bash.

You also get full control of the appearance of the shells including the font, color, etc… Cmder has many themes, but the default Monokai theme is good enough for me.

More importantly, you can create custom tasks. A custom task is a specific command window that you can define. You can specify the shell, what parameters it’s called with, and what directory is opened. You can have a command line setup for each application you work on. You no longer need to open a command line and manually navigate to your app folder each time you open up the console.

To make a custom task, do the following:

From Cmder, type Win + Alt + T. This takes you the tasks windows. You can also click the arrow next to the plus sign and click “Setup Tasks”.

This window allows you to reorder and reorganize the different defaults in Cmder. Hit the plus sign to add your own.

In this case, this is a console task that opens a specific project I’m working on.

After you setup your new task, click “Save Settings”. You should see your new shell in the list of available presets. Then you can open that exact shell whenever you want.

If you want to supercharge your Windows console, check out Cmder.