Why does TraversableOnce.toSeq return a stream?

Question

Here is an example:

scala> val xs = List(1,2,3).toIterator.toSeq
xs: Seq[Int] = Stream(1, ?)

A sequence is a materialized set (the default is a List), so I expected to toSeqreturn List, notStream

The implementation is done in TraversableOnce,

  def toSeq: Seq[A] = toStream

why is it not redefined in TraversableLike?

+4

Adrian Oct 17 '14 at 19:31

1 answer

bmaderbacher · Accepted Answer · 2014-10-17T21:24:47+0000

Scala supports infinite iterators, and Streamis the easiest Seqfor possible infinite data.

Iterator.from(1).toSeq

ends (if only part of the collection is used), but

Iterator.from(1).toList

will never end.

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