Scala case class this()

Question

I'm using several case classes in my scala project (scala 2.10). I'm also using the jacoco code coverage tool, version 2.1.2.

When jacoco looks at a simple case class, e.g.

case class TestClass( val x : Int )
{
    def double() : Int = x * 2
}

it reports a method of the auto-generated object called this(), which takes no parameters. Obviously, my class takes a single parameter. The only way I can satisfy jacoco that this method is tested is by having a test such as this:

test( "Case class test" )
{
    TestClass
}

My main questions are:

• Is a no-argument this method actually generated for a case class' companion object, or is it a jacoco bug?
• If the former, what functionality does it provide? What's the correct way to test it?

Thanks.

N.B. as an aside, I believe upgrading to jacoco 2.1.3 may solve this, but that's not currently an option for me.

Answer 1

I assume that this is a representation for constructors, since there's no method with that name generated from that, and the only such constructor is in the companion object.

It has to exist because the companion object has to be created. It is private, because the companion object is created as a singleton. Note also that objects are only instantiated on demand, so it makes sense that it didn't get tested if you didn't use the companion object.

However, even a simple instantiation of TestClass ought to use that:

val x = TestClass(5)

That calls a method on the TestClass companion object, which, in turn, causes that object to be instantiated.