Scala represent an Option tuple

Question

How to explicitly set an Option which is a tuple of a certain type to be None?

scala> var c = Some(1,1)
c: Some[(Int, Int)] = Some((1,1))

scala> c = None
<console>:11: error: type mismatch;
 found   : None.type
 required: Some[(Int, Int)]
       c = None
           ^

scala> None()
<console>:11: error: None.type does not take parameters
       None()
           ^

scala> c = None()
<console>:11: error: None.type does not take parameters
       c = None()
               ^

scala> c = None.Int
<console>:11: error: value Int is not a member of object None
       c = None.Int
                ^

scala> c = None(Int, Int)
<console>:11: error: None.type does not take parameters
       c = None(Int, Int)
               ^

scala> c = (None, None)
<console>:11: error: type mismatch;
 found   : (None.type, None.type)
 required: Some[(Int, Int)]
       c = (None, None)

Just declare the type explicitly at first usage. The inference is too precise/restrictive here - Some instead of Option. var c: Option[(Int, Int)] = Some((1,1)) — Didier Dupont, Nov 02 '15 at 14:45

Zoltán · Accepted Answer · 2015-11-02T17:43:48.880

10

As @DidierDupont pointed it out - your first declaration of c infers that its type is Some[(Int, Int)], instead of Option[(Int, Int)]. Declare c as the following and you should be fine:

var c: Option[(Int, Int)] = Some((1, 1))

or, as Gabriele Petronella pointed out, simply

var c = Option((1, 1))

edited Nov 02 '15 at 17:43

answered Nov 02 '15 at 14:49

Zoltán

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or just `val c: Option((1, 1))`. Also this is using auto-tupling, which might not be the best idea here – Gabriele Petronella Nov 02 '15 at 15:16
What Gabriele said, plus this explanation - http://stackoverflow.com/a/5998559/409976. – Kevin Meredith Nov 02 '15 at 17:26
1

@KevinMeredith I've removed auto-tupling. Thanks for the reference. – Zoltán Nov 02 '15 at 17:44

score 2 · Answer 2 · answered Nov 02 '15 at 14:51

2

You declared c = Some(1,1) which set the type to Some. You really wanted a type of Option, so try by declaring the type:

var c:Option[(Int,Int)] = Some(1,1)
c = None

answered Nov 02 '15 at 14:51

Keith Pinson

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What is the type is a return parameter of a method? – joesan Nov 02 '15 at 14:52
If the method is defined to return type, Some, you can still declare the variable as type Option. – Keith Pinson Nov 02 '15 at 15:01

score 0 · Answer 3 · answered Nov 02 '15 at 14:54

Actually this is not about tuples. Following code will not work:

var a = Some("String")
a = None

because Scala has a type Some[T] which is a subclass of Option[T] just like None, this means Some[T] and None types are at same inheritance level. So from this we can say that declaring type explicitly as others mentioned will do work.

var a: Option[(Int, Int)] = Some((1, 1))

you can check more if you want at: Scala Option

Scala represent an Option tuple

3 Answers3