The identity for the cons operator in scala

Question

Is there any x such that:

x :: List(n) == List(n)

or

x :: List(n, n + 1, n + 2) == List(n, n + 1, n + 2)

I thought Nil would do this, but it doesn't. It seems to work when I do:

n :: Nil

or

List(n, n + 1, n + 2) :: Nil

but I need it the other way around.

Do you really mean `x :: n == List(n)` in the first example or rather `x :: n == n`? — sepp2k, Aug 28 '18 at 14:28
it doesn't have to be the cons operator, but I just need some way to append nothing to a List from the left hand side. — user3685285, Aug 28 '18 at 14:31

Tim · Accepted Answer · 2018-08-28T15:37:21.090

4

You want the ::: or ++ operator, which will concatenate two lists:

Nil ::: List(n)
Nil ++ List(n)

Andrey helpfully points out that the ++ operator is more generic, so check out this link that he provided in his comment.

edited Aug 28 '18 at 15:37

answered Aug 28 '18 at 14:32

Tim

2

[`::: vs ++`](https://stackoverflow.com/questions/6559996/scala-list-concatenation-vs) – Andrey Tyukin Aug 28 '18 at 15:18
1

You should directly include the link in the answer, since the comments might go away at any time. – Ethan Aug 28 '18 at 15:35

1 Answers1