Why is flatten declared on GenericTraversableTemplate and not TraversableLike

BTW - if I have posted this on the wrong list (possibly it belongs on scala user) then let me know

From: oxbow_lakes@hotmail.com
To: scala-internals@listes.epfl.ch
Subject: [scala-internals] Why is flatten declared on GenericTraversableTemplate and not TraversableLike
Date: Fri, 27 Nov 2009 14:57:27 +0000

.ExternalClass .ecxhmmessage P {padding:0px;} .ExternalClass body.ecxhmmessage {font-size:10pt;font-family:Verdana;} I asked this on StackOverflow but it had no response. (http://stackoverflow.com/questions/1802828/why-is-flatten-declared-on-ge...).



The signature of TraversableLike.flatMap is as follows:

def flatMap[B, Th](f : (A) => Traversable[B])(implicit bf : CanBuildFrom[Repr, B, Th]) : Th

The signature of GenericTraversableTemplate.flatten is:

def flatten[B](implicit asTraversable : (A) => Traversable[B]) : CC[B]

Why is the latter method (which seems to me to differ in usage from flatMap only in the sense that the transformer function is implicit) not definable on TraversableLike as:

def flatten[B, Th](implicit asTraversable: (A) => Traversable[B], 
                   implicit bf : CanBuildFrom[Repr, B, Th]) : Th

Is there some reason that this must be the case?


Chris


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Indeed, by analogy to flatMap, this might be a better signature (&implementation) for flatten in TraversableLike:
  def flatten[B](implicit asTraversable: A => Traversable[B], bf: CanBuildFrom[Repr, B, That]): That = flatMap(asTraversable)
If no-one objects, I'll remove the old flatten implementation and move this one-liner to TraversableLike

cheers
adriaan