Pragmatic Scala

Value Classes

Code like 2 days ago is charming, but what’s the catch? Let’s take a look under the hood to see what the Scala compiler actually did to that expression. Compile the file DateUtil.scala using scalac and run javap -c UseDateUtil\$, the shadow inner class that Scala created for the singleton, and quickly search for the call to the days method. Let’s examine a few lines of bytecode around the method call:

Here’s the cost of the ...