Getting started with the Scala REPL (command-line shell) alvin June 20, 2015 - 4:07pm

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 14.1, “How to get started with the Scala REPL.”

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You want to get started using the Scala REPL, including understanding some of its basic features, such as tab completion, starting the REPL with different options, and dealing with errors.

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To start the Scala REPL, type scala at your operating system command line:

Table of Contents

  1. Problem
  2. Solution
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Scala SBT: How to “re-run with -deprecation” (or -feature)

Scala FAQ: When compiling a Scala application with SBT, I get warning messages like these:

$ sbt compile

[warn] there were 6 deprecation warnings; re-run with -deprecation for details
[warn] there were 4 feature warnings; re-run with -feature for details

How do I ’re-run with -deprecation’ or ’re-run with -feature’?

Scala REPL: There were deprecation warnings, re-run with -deprecation

Whenever I used to get the Scala REPL warning message, "There were deprecation warnings, re-run with -deprecation", I used to have to restart the REPL with the -deprecation flag to see the warning message, like this:

$ scala -deprecation

That works, but sadly, you had to lose your entire REPL session to run it.

Use :warnings

Thanks to the Scala gods, this is no longer necessary in Scala 2.10 (and newer). Now, when you get the REPL deprecation warning message, like this: