Programming Scala, 2nd Edition

Chapter 14. Scala’s Type System, Part I

Scala is a statically typed language. Its type system is arguably the most sophisticated in any programming language, in part because it combines comprehensive ideas from functional programming and object-oriented programming. The type system tries to be logically comprehensive, complete, and consistent. It fixes several limitations in Java’s type system.

Ideally, a type system would be expressive enough that you could prevent your program from ever “inhabiting” an invalid state. It would let you enforce these constraints at compile time, so runtime failures would never occur. In practice, we’re far from that goal, but Scala’s type system pushes the boundaries toward this long-term goal.

However, the type system can be intimidating at first. It is the most controversial feature of the language. When people claim that Scala is “complex,” they usually have the type system in mind.

Fortunately, type inference hides many of the details. Mastery of the type system is not required to use Scala effectively, although you’ll eventually need to be familiar with most constructs.

We’ve already learned a lot about the type system. This chapter ties these threads together and covers the remaining, widely used type system features that every new Scala developer should learn. The next chapter covers more advanced features that aren’t as important to learn immediately if you’re new to Scala. When we get to Chapter 24, we’ll discuss type information in the ...