Programming Scala, 2nd Edition

Chapter 3. Rounding Out the Basics

Let’s finish our survey of essential “basics” in Scala.

Operator Overloading?

Almost all “operators” are actually methods. Consider this most basic of examples:

1 + 2

That plus sign between the numbers? It’s a method.

First, note that all the types that are special “primitives” in Java are actually regular objects in Scala, meaning they can have methods: Float, Double, Int, Long, Short, Byte, Char, and Boolean.

As we’ve seen, Scala identifiers can have nonalphanumeric characters, with a few exceptions that we’ll go over in a moment.

So, 1 + 2 is the same as 1.+(2), because of the “infix” notation where we can drop the period and parentheses for single-argument methods.¹

Similarly, a method with no arguments can be invoked without the period. This is called “postfix” notation. However, use of this postfix convention can sometimes be confusing, so Scala 2.10 made it an optional feature. We set up the SBT build to trigger a warning if we use this feature without explicitly telling the compiler we want to use it. We do that with an import statement. Consider the following REPL session using the scala command (versus SBT console):

$ scala
...
scala> 1 toString
warning: there were 1 feature warning(s); re-run with -feature for details
res0: String = 1

Well, that’s not helpful. Let’s restart REPL with the -feature flag to produce a more informative warning:

$ scala -feature
...
scala> 1.toString  // normal invocation
res0: String = 1

scala> 1