Chapter 1: An Introduction to Crystal

Crystal is a safe, performant, general-purpose, and object-oriented language. It was heavily inspired by Ruby's syntax and Go's and Erlang's runtimes, enabling a programmer to be very productive and expressive while creating programs that run efficiently on modern computers.

Crystal has a robust type system and can compile to native programs. Consequently, most programming errors and mistakes can be identified at compile time, giving you, among other things, null safety. Having types doesn't mean you have to write them everywhere, however. Crystal relies on its unique type interference system to identify the types of almost every variable in the program. Rare are the situations where the programmer has to write an explicit type somewhere. But when you do, union types, generics, and metaprogramming help a lot.

Metaprogramming is a technique where a structured view of the written program is accessed and modified by the program itself, producing new code. This is a place where Ruby shines with all its dynamism and built-in reflection model, and so does Crystal, in its own way. Crystal is capable of modifying and generating code during compilation time with macros and a zero-cost static reflection model. It feels like a dynamic language in every way, but it will compile the program down to pure and fast machine code.

Code written in Crystal is expressive and safe, but it's also fast – really fast. Once built, it goes head to head with other low-level languages such as C, C++, or Rust. It beats pretty much any dynamic language and some compiled languages too. Although Crystal is a high-level language, it can consume C libraries with no overhead, the lingua franca of system programming.

You can use Crystal today. After 10 years of intense development and testing, a stable and production-ready version was released in early 2021. Alongside it, a complete set of libraries (called "shards") are available, including web frameworks, database drivers, data formats, network protocols, and machine learning.

This chapter will introduce a brief history of the Crystal language and present some of its characteristics regarding performance and expressiveness. After that, it will bring you up to speed by explaining how to create and run your first Crystal program. Finally, you will learn about some of the challenges for the future of the language.

In particular, we will cover the following topics:

• A bit of history
• Exploring Crystal's expressiveness
• Crystal programs are also FAST
• Creating our first program
• Setting up the environment

This should get you started on what Crystal is, understanding why it should be used, and learning how to execute your first program. This context is essential for learning how to program in Crystal, going from small snippets to fully functional and production-ready applications.