Chapter 10. Dialyzer and type specifications
This chapter covers
- What Dialyzer is and how it works
- Finding discrepancies in your code with Dialyzer
- Writing type specifications and defining your own types
Depending on your inclination, the mere mention of types may make you either shriek with joy or recoil in terror. Being a dynamically typed language, Elixir spares you from having to pepper your code base with types à la Haskell. Some may argue that this leads to a quicker development cycle. But Elixir programmers shouldn’t be too smug. Statically typed languages can catch an entire class of errors at compile time that a dynamic language can only catch at runtime.
Fortunately, the fault-tolerance features baked into the language try to save us from ourselves. Languages without these features (Ruby, I’m looking at you) will crash. But it’s your responsibility to make your software as reliable as possible. In this chapter, you’ll learn how to exploit types to do that.
You’ll be introduced to Dialyzer, a tool that comes bundled with the Erlang distribution. This power tool is used to weed out certain classes of software bugs. The best part? You don’t have to do anything special to your code.
You’ll learn some of the interesting theory behind how Dialyzer works, which will help you decipher its (sometimes cryptic) error messages. I’ll also explain why Dialyzer isn’t a silver bullet to solve all of your typing woes.