“Subclasses” of AnyVal do not behave properly from a hashing perspective:
scala> 1.0.hashCode
res14: Int = 1072693248
Of course this is boxed to a call to:
scala> new java.lang.Double(1.0).hashCode
res16: Int = 1072693248
We might prefer it to be:
scala> new java.lang.Double(1.0).##
res17: Int = 1
scala> 1.0.##
res15: Int = 1
We should expect this given that the int 1 is also the double 1. Of course this issue does not arise in Java. Without it, we’d have this problem:
Set(1.0) contains 1 //compiles but is false
Luckily:
scala> Set(1.0) contains 1
res21: Boolean = true