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I'm developing a Scala package using an sbt project scheme through IntelliJ. I wanted to use the classes in this package in the Scala REPL, so I followed the instructions in this post. Namely,

  1. Navigate to where my package's source files are located (MyProject/src/main/scala/mypackage)
  2. Run "sbt compile"
  3. Navigate to where sbt stores the compiled source files (MyProject/src/main/scala/mypackage/target/scala-2.12/classes/mytest)
  4. Run "scala -cp ."

This all works fine until I try to create an instance of one of my package's classes and I get the error MyClass does not have a constructor. However, if I just paste the class definitions into the Scala REPL, I can create instances with no errors. What am I doing wrong here?

As a reproducible example, I created a package mytest with two files TraitOne.scala and ClassOne.scala. The first file looks like

package mytest

trait TraitOne {
  val a: Double
  def aMinus(x: Double): Double = a - x
}

The second file looks like

package mytest

class ClassOne(val a: Double) extends TraitOne {
  def aPlus(x: Double): Double = a + x 
}

If I follow steps 1 - 4 as listed above and write val temp = new ClassOne(1.0), I get the error ClassOne does not have a constructor. But if I paste

trait TraitOne {
  val a: Double
  def aMinus(x: Double): Double = a - x
}
class ClassOne(val a: Double) extends TraitOne {
  def aPlus(x: Double): Double = a + x 
}

into the REPL, val temp = new ClassOne(1.0) works fine.

zack
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    Why not just run `sbt console`? Or, if you want to use those classes on other environments, try `sbt package` to generate a single **JAR** with all your classes, and then pass that **JAR** to the `cp` argument. – Luis Miguel Mejía Suárez Dec 01 '19 at 01:27
  • I tried the JAR method, navigating to `MyProject/src/main/scala/mypackage` and running `sbt package`. This was successful, and a `.jar` file appeared at `MyProject/src/main/scala/mypackage/target/scala-2.12/classes/mypackage_2.12-0.1.0-SNAPSHOT.jar`. However, when I run `scala -cp pathtojar`, neither `import mypackage` nor `val temp = new ClassOne(1.0)` work. Any thoughts? – zack Dec 02 '19 at 17:58
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    Why exactly do you need this? If you just want to have a **REPL** with your classes you can always use `sbt console`. If you want to distribute your classes to other users, there are other alternatives. – Luis Miguel Mejía Suárez Dec 02 '19 at 18:15
  • To answer your question - I'm writing a package while reading a Scala textbook to put the concepts to practice. It might be bad practice (please tell me if it is), but I was planning on playing with the package's classes as I create them in order to gauge user friendliness / feature completeness. I tried your suggestion of `sbt console` from within `MyProject` and it worked! Thanks so much for your advice. – zack Dec 03 '19 at 04:14
  • Zack, that is pretty cool. Yesterday I was already falling of sleep and I read your last message wrong. You said that `sbt console` worked and somehow I understood that it didn't work. I am glad it helped. I deleted my last comment _(since it doesn't make sense anymore)_ I would suggest you do the same with your last comment since it is off-topic to the site right now. – Luis Miguel Mejía Suárez Dec 03 '19 at 13:42

1 Answers1

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Run scala -cp MyProject/src/main/scala/mypackage/target/scala-2.12/classes

Don't include the package in classpath

joeljohansson
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