In Scala 3, all kinds of definitions can be written at the “top level” of your source code files. For instance, you can create a file named MyCoolApp.scala and put these contents into it:
import scala.collection.mutable.ArrayBuffer enum Topping: case Cheese, Pepperoni, Mushrooms import Topping.* class Pizza: val toppings = ArrayBuffer[Topping]() val p = Pizza() extension (s: String) def capitalizeAllWords = s.split(" ").map(_.capitalize).mkString(" ") val hwUpper = "hello, world".capitalizeAllWords type Money = BigDecimal // more definitions here as desired ... @main def myApp = p.toppings += Cheese println("show me the code".capitalizeAllWords) As shown, there’s no need to put those definitions inside a package, class, or other construct.
Replaces package objects
If you’re familiar with Scala 2, this approach replaces package objects. But while being much easier to use, they work similarly: When you place a definition in a package named foo, you can then access that definition under all other packages under foo, such as within the foo.bar package in this example:
package foo { def double(i: Int) = i * 2 } package foo { package bar { @main def fooBarMain = println(s"${double(1)}") // this works } } Curly braces are used in this example to put an emphasis on the package nesting.
The benefit of this approach is that you can place definitions under a package named com.acme.myapp, and then those definitions can be referenced within com.acme.myapp.model, com.acme.myapp.controller, etc.