Learning Scala

Chapter 4. Functions

Functions are the core building blocks of reusable logic. Of course, you probably already knew that, because nearly all other languages also have functions (or methods, the object-oriented version of functions). Devoting an entire chapter to a concept common across languages may thus seem odd, but to Scala and other functional programming languages functions are very important.

Functional programming languages are geared to support the creation of highly reusable and composable functions and to help developers organize their code base around them. Much like a Unix power user will compose multiple single-purpose tools into a complex piped command, a functional programmer will combine single-purpose function invocations into chains of operations (think Map/Reduce). A function that was written with a simple purpose (e.g., to double a number) may be picked up and applied across a 50,000-node list, or given to an actor to be executed locally or in a remote server.

In Scala, functions are named, reusable expressions. They may be parameterized and they may return a value, but neither of these features are required. These features are, however, useful for ensuring maximum reusability and composability. They will also help you write shorter, more readable, and more stable applications. Using parameterized functions you can normalize duplicated code, simplifying your logic and making it more discoverable. Testing your code becomes easier, because normalized and parameterized ...