Imported From: https://issues.scala-lang.org/browse/SI-3749?orig=1
Reporter: @acruise

@lrytz said:
Note that

scala> List(1.0, 2l)
res1: List[Double] = List(1.0, 2.0)

@adriaanm said:
We plan to address this issue in future versions of Scala by introducing union types, so that the approximation of the least upper bound you see here could be denoted directly (and precisely) as java.lang.Double or java.lang.Long.

The current Scala compiler must approximate this type by expanding it, and truncating when it's gone two levels deep (to avoid even longer types -- in principle, the expansion is infinite).

First, we need to work out the nitty gritty details of the theory, though.