It appears the toSeq method in Scala collections returns a scala.collection.Seq, I could also return a Traversable or Iterable but need to convert this to a scala.collection.immutable.Seq.
Is there an easy way to do this?
Thanks Richard
asked Jun 5, 2013 at 12:09
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1 Answer
Use the to method to convert between arbitrary collection types in Scala 2.10:
scala> Array(1, 2, 3).toSeq
res0: Seq[Int] = WrappedArray(1, 2, 3)
scala> Array(1, 2, 3).to[collection.immutable.Seq]
res1: scala.collection.immutable.Seq[Int] = Vector(1, 2, 3)
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1Your answer helped me, but WHY, oh why is this even needed? I'm only working with immutable collections - how come a result of for-yield would need such a .to?– akauppiCommented Jun 14, 2016 at 7:14
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2My friend, Ivan Yurchenko clarified this: The problem is that there are three things: A) scala.collection.Seq B) scala.collection.immutable.Seq C) scala.collection.mutable.Seq B and C derive from A so, if we have A, we can't surely say if it's mutable or immutable, that's why explicit conversion (.toList or something) or setting them immutable from the beginning is needed– akauppiCommented Jun 14, 2016 at 8:20
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1It's just weird because the default Seq in Scala is just collections.Seq; which is odd because mostly, everything is immutable. List(1,2,3).toSeq generates a collections.Seq... not immutable.collections.Seq. Doesn't that seem wrong?– PlexQCommented May 30, 2018 at 5:42
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and even more weirdly - a immutable.collections.Seq .toIterable yields a collections.Iterable, NOT a immutable.collections.Iterable!– PlexQCommented May 30, 2018 at 5:44