Design patterns are the negative space of a programming language. They are the techniques that programmers come up with to effectively leverage a language's strengths and compensate for its weaknesses. We all use them whether we mean to or not. The classic Gang of Four Design Patterns book took existing patterns that were already being used in the wild and catalogued and classified them. Perhaps even more importantly, it gave them names so that programmers could refer to common patterns easily and immediately understand each other. It gave programmers a lingua franca for the tools of their trade.
Whereas classic design pattern books have focused almost exclusively on patterns themselves, assuming language proficiency as a given, Hands-on Design Patterns and Best Practices with Julia weaves together both the positive and negative space images of Julia. It introduces the language features that patterns depend on as they are used, making the book accessible even for readers who are not already fluent Julia programmers. This approach provides a comprehensive introduction of the language, while also covering advanced subjects as the book progresses. The later chapters delve into the kinds of sophisticated design patterns used by Julia wizards, so by the time you get to the end, you will truly have mastered the language. Be forewarned, however, as with most of the best programming books, it may require more than one read through before you've fully digested the content.
One of the more interesting aspects of creating a widely used programming language is seeing the remarkable and surprising things that people do with it. This includes incredible and sometimes world-changing applications that people have built in Julia—from specifying the FAA's next generation air collision avoidance system, to mapping all the visible universe's celestial bodies, to modeling climate change with unprecedented accuracy and resolution. But it also includes the clever programming tricks that people come up with to make it do their bidding. One of my favorites is the (Tim) Holy Trait Trick, discussed in Chapter 5, Reusability Patterns, which leverages the fact that Julia can efficiently dispatch on as many arguments as we want, to work around the language's lack of multiple inheritance. Not only does this technique get the job done, it goes well beyond: traits can depend on computed properties of types, allowing them to express relationships that multiple inheritance cannot. It turns out that the language already had the expressive power that was needed, it just took a clever design pattern to unlock it.
Tom's background gives him an expertly nuanced and balanced perspective on programming languages and their design patterns. He started programming in BASIC. But since those early days, he's used a broad variety of languages in professional settings, including: C++, Java, Python, TypeScript, Scheme and—of course—Julia. The set of technological sectors he's applied these languages in are equally diverse: finance, search engine, e-commerce, content management, and currently asset management. Perhaps not coincidentally, Julia is gaining significant traction in many of these sectors, especially those which are computationally demanding. Our backgrounds shape how we see the world and sometimes you find a new tool that feels like it was made for you. Sometimes you encounter a new programming language and think This is how I've always wanted to write programs! Julia has been that language for Tom and for many others. Hopefully it will be for you as well. Whether you are just trying Julia for the first time, or have used it for years and want to level up with more advanced techniques, you will find what you're looking for in this book. Enjoy and happy coding!
Stefan Karpinski
Co-creator of the Julia programming language
Co-founder of Julia Computing, Inc.