Pragmatic Scala

The Omnipresent Underscore Character

That little character _ (underscore) seems to be everywhere in Scala—you’ve seen it a few times in this book so far; it’s probably the most widely used symbol in Scala. Knowing the different places where it’s used can alleviate surprises when you encounter it the next time. Here’s a list of various uses of the symbol.

The _ symbol may be used:

• as a wildcard in imports For example, import java.util._ is the Scala equivalent of import java.util.* in Java.

• as a prefix to index a tuple Given an tuple val names = ("Tom", "Jerry") you can access the two values using the syntax names._1 and names._2, respectively.

• as implied arguments to a function value The code list.map { _ * 2 } is equivalent to list.map { e ...