Software Design Patterns: Introduction

Throughout my career, I kept finding myself writing code for solutions that, on the surface, looked increasingly similar to things I’d written before. What I didn’t realise at the time was that I was inadvertently implementing patterns that have existed in software engineering for decades—the Gang of Four design patterns.

Once I noticed this, I discovered most of these patterns were already well-documented on sites like Wikipedia. But I’d never actually sat down to learn them properly from scratch, stepping through each one with a debugger to understand how they really work.

There was another problem: working examples in C# were almost impossible to find. Most resources contained diagrams only, and the code samples that did exist were written in Java or other languages. What I wanted was dependency-free sample code that I could set a breakpoint in and watch execute, line by line.

So I sat down and worked through a 15-hour Pluralsight course on the subject, writing up each pattern as I went. This gave me both a learning exercise and a reference to return to later.

Working C# examples for every pattern in this series are available on GitHub:

maceage/design-patterns

The Gang of Four patterns

The patterns fall into three broad categories:

Rather than one enormous post listing every pattern, each one gets its own detailed write-up:

• Creational
  • Builder pattern
  • Factory pattern
  • Lazy Load pattern
    • Ghosts
    • Lazy Init
    • Value Holder
    • Virtual Proxy
  • Prototype pattern
  • Singleton pattern
• Structural
  • Adapter pattern
  • Bridge pattern
  • Composite pattern
  • Decorator pattern
  • Façade pattern
  • Flyweight pattern
  • Marker pattern
  • Proxy pattern
  • Repository pattern
• Behavioural
  • Chain of Responsibility pattern
  • Command pattern
  • Event Aggregator pattern
  • Interpreter pattern
  • Iterator pattern
    • Iterator example
    • Tree example
  • Mediator pattern
  • Memento pattern
  • Null Object pattern
  • Observer pattern
    • Traditional
    • IObserver
    • EventDelegate
  • Rules pattern
  • State pattern
  • Strategy pattern
  • Template Method pattern
  • Visitor pattern