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scalashrinkscalacheck

Shrink macro for case class

I'm implementing Shrink instances for my case classes. It seems to me that a macro could do the job. Has someone implemented one yet?

Solution

  • Yes, they have! shapeless-contrib has an instance of Shapeless's TypeClass for Shrink:

    scala> import org.scalacheck._
import org.scalacheck._

scala> case class Foo(s: String, i: Int)
defined class Foo

scala> val unshrunk = Foo("This is a very long string", 1000)
unshrunk: Foo = Foo(This is a very long string,1000)

scala> implicitly[Shrink[Foo]].shrink(unshrunk) // boring default instance
res0: Stream[Foo] = Stream()

scala> import shapeless.contrib.scalacheck._
import shapeless.contrib.scalacheck._

scala> implicitly[Shrink[Foo]].shrink(unshrunk) // interesting instance
res1: Stream[Foo] = Stream(Foo(This is a ver,1000), ?)

    This is supported by macros, but only the ones that Shapeless uses for its Generic machinery.