Scala - ordering a list

I am trying to sort a List of XMLMessage which in turn, derive from Message. The Message trait extends Ordered and provides comparison function based on timestamps. However, when I try to say:

list.sorted

the error says

error: diverging implicit expansion for type scala.math.Ordering[domain.XMLMessage]
starting with method comparatorToOrdering in trait LowPriorityOrderingImplicits

How can I provide ordering on the Messages so that list.sorted would work? Thanks

Answers


sorted requires an Ordering[XMLMessage], but you (through implicits) can only provide an Ordering[Message]. Ordering is invariant, hence the sort cannot use it. The easiest way to achieve what you want is probably:

list.sortBy(_: Message)

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