Dmitri Nesteruk - Design Patterns in .NET Core 3: Reusable Approaches in C# and F# for Object-Oriented Software Design

Any source code or other supplementary material referenced by the author in this book is available to readers on GitHub via the books product page, located at www.apress.com/9781484261798 . For more detailed information, please visit http://www.apress.com/source-code .

The topic of Design Patterns sounds dry, academically dull, and, in all honesty, done to death in almost every programming language imaginable including programming languages such as JavaScript which arent even properly object-oriented! So why another book on it? I know that if youre reading this, you probably have a limited amount of time to decide whether this book is worth the investment.

I decided to write this book to fill a gap left by the lack of in-depth patterns books in the .NET space. Plenty of books have been written over the years, but few have attempted to research all the ways in which modern C# and F# language features can be used to implement design patterns, and to present corresponding examples. Having just completed a similar body of work for C++, I thought it fitting to replicate the process with .NET.

Now, on to design patterns the original Design Patterns book was published with examples in C++ and Smalltalk, and since then, plenty of programming languages have incorporated certain design patterns directly into the language. For example, C# directly incorporated the Observer pattern with its built-in support for events (and the corresponding event keyword).

Design Patterns are also a fun investigation of how a problem can be solved in many different ways, with varying degrees of technical sophistication and different sorts of trade-offs. Some patterns are more or less essential and unavoidable, whereas other patterns are more of a scientific curiosity (but nevertheless will be discussed in this book, since Im a completionist).

Readers should be aware that comprehensive solutions to certain problems often result in overengineering, or the creation of structures and mechanisms that are far more complicated than is necessary for most typical scenarios. Although overengineering is a lot of fun (hey, you get to fully solve the problem and impress your co-workers), its often not feasible due to time/cost/complexity constraints.

This book is designed to be a modern-day update to the classic Gang of Four (GoF, named after the four authors of the original Design Patterns book) book, targeting specifically the C# and F# programming languages. My focus is primarily on C# and the object-oriented paradigm, but I thought it fair to extend the book in order to cover some aspects of functional programming and the F# programming language.

The goal of this book is to investigate how we can apply the latest versions of C# and F# to the implementation of classic design patterns. At the same time, its also an attempt to flesh out any new patterns and approaches that could be useful to .NET developers.

Finally, in some places, this book is quite simply a technology demo for C# and F#, showcasing how some of the latest features (e.g., default interface methods) make difficult problems a lot easier to solve.

You should be aware that most of the examples leverage the latest version of C# and generally use the latest C# language features that are available to developers. For example, I use dynamic , pattern matching, and expression-bodied members liberally.

At certain points in time, I will be referencing other programming languages such as C++ or Kotlin. Its sometimes interesting to note how designers of other languages have implemented a particular feature. C# is no stranger to borrowing generally available ideas from other languages, so I will mention those when we come to them.

As I write this book, the streets outside are almost empty. Shops are closed, cars are parked, public transport is rare and empty too. Life is almost at a standstill as the country endures its first nonworking month, a curious occurrence that one (hopefully) only encounters once in a lifetime. The reason for this is, of course, the COVID-19 pandemic that will go down in the history books. We use the phrase stop the world a lot when talking about the garbage collector, but this pandemic is a