CODEWITHSUNDEEP
scalacompiler-errorspattern-matching
Paul Draper
Paul Draper

Reputation: 83411

error: not found: value :::

I can create a list like so:

val value = List(1) ::: 2 :: List(3)

Now I am trying to decompose that list like so:

value match { case a ::: b :: c => (a, b, c) }

but I get error: not found: value :::.

Why I am getting this error. Why doesn't this pattern work, and what should I use instead?

Upvotes: 1

Views: 1089

Answers (1)

Odomontois
Odomontois

Reputation: 16328

Suppose you have 

val xs = List(1, 2, 3, 4)

and suppose there is an extractor object that could extract a collection prefix. What should be matched for 

case a ::: b :: c => (a, b, c)

Is it (choose all that apply)

  • (List(1, 2, 3), 4, Nil)
  • (List(1, 2), 3, List(4))
  • (List(1), 2 , List(3, 4))
  • (Nil, 1, List(2, 3, 4))

Because there is more than one way of matching the pattern, the above extractor cannot exist. Instead you could use the following.

value match { case a :: b :: c => (List(a), b, c) }

Upvotes: 3

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