Programming Scala, 2nd Edition

Chapter 2. Type Less, Do More

We ended the first chapter with a “teaser” example of an Akka actor application. This chapter continues our tour of Scala features, focusing on features that promote succinct, flexible code. We’ll discuss organization of files and packages, importing other types, variable and method declarations, a few particularly useful types, and miscellaneous syntax conventions.

Semicolons

Semicolons are expression delimiters and they are inferred. Scala treats the end of a line as the end of an expression, except when it can infer that the expression continues to the next line, as in this example:

// src/main/scala/progscala2/typelessdomore/semicolon-example.sc

// Trailing equals sign indicates more code on the next line.
def equalsign(s: String) =
  println("equalsign: " + s)

// Trailing opening curly brace indicates more code on the next line.
def equalsign2(s: String) = {
  println("equalsign2: " + s)
}

// Trailing commas, periods, and operators indicate more code on the next line.
def commas(s1: String,
           s2: String) = Console.
  println("comma: " + s1 +
          ", " + s2)

Compared to the compiler, the REPL is more aggressive at interpreting the end of a line as the end of an expression, so when entering a multiline expression, it’s safest to end each line (except for the last) with one of the indicators shown in the previous script.

Conversely, you can put multiple expressions on the same line, separated by semicolons.

Tip

Use the REPL’s :paste mode when semicolon inference ...