Question

I’ve seen some blogs on the Pimp my Library pattern, and these seem to work well for adding behavior to classes.

But what if I have a case class and I want to add data members to it? As a case class I can’t extend it (inheriting from a case class is deprecated/strongly discouraged). Will any of these pimp patterns allow me to add data to a case class?

Answer 1

No – I don’t see how you could make this work because the enriched instance is usually thrown away (note: newly the pimp-my-library pattern is called enrich-my-library). For example:

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

scala> implicit class Y(x: X)  {
   |     var f: Float = 0F
   |   }
defined class Y

scala> X(1, "a")
res17: X = X(1,a)

scala> res17.f = 5F
res17.f: Float = 0.0

scala> res17.f
res18: Float = 0.0

You would have to make sure you kept hold of the wrapped instance:

scala> res17: Y
res19: Y = Y@4c2d27de

scala> res19.f = 4
res19.f: Float = 4.0

scala> res19.f
res20: Float = 4.0

However, I find this not useful in practice. You have a wrapper; you’re better off making this explicit