Scala generic (tuple) type with multiple subtypes

Question

I am writing a data structure (basically a hashmap) in Scala that will take one tuple (of possibly different number of arguments each time) and do something with it. To generically implement this, I defined a type:

type T <: Tuple1[_] with Tuple2[_,_] with Tuple3[_,_,_] with Tuple4[_,_,_,_] with Tuple5[_,_,_,_,_]

and then the data structure

val map = new HashMap[Int, T]

But this is ugly, since I have to change the type every time I have to handle more arguments in a tuple. Is there to define a generic tuple type?

Thanks, Y.K.

Maybe you will be happy with Product? Yes, it allows to pass-in not only tuples, but it is pretty generic — om-nom-nom
– om-nom-nom, Commented Dec 9, 2012 at 9:38
Why do you restrict the value type of your data structure specifically to tuples? Do you intend to exploit some property common to all tuple types? — n. m. could be an AI
– n. m. could be an AI, Commented Dec 9, 2012 at 10:28
Thank you for your replies. I restrict the ds to tuples, since this is what the user will eventually enter (e.g. (3, 4.5, "foo")), and i want to avoid type conversions. I could use Product yes, however then I would have to have a regexp matching for the different types when i get each T back right? Something like varT match { case (,) => ... case (,,_) => ... } and so on... right? — Y.K.
– Y.K., Commented Dec 9, 2012 at 10:35
I'm not sure I understand exactly what you're trying to do, but generalizing over tuple arity (without giving up type safety) is painful in Scala without the help of something like a heterogenous list implementation (I'd recommend Shapeless's). — Travis Brown
– Travis Brown, Commented Dec 9, 2012 at 12:03
I don't see which type conversions would be eliminated. Can you point out some? If the user will eventually enter (subtypes of) Any, would restricting T to Any eliminate type conversions? — n. m. could be an AI
– n. m. could be an AI, Commented Dec 9, 2012 at 13:16

Lomig Mégard · Accepted Answer · 2012-12-09 12:05:49Z

4

The first solution is to use Product, as said by @om-nom-nom. Indeed, it's the only common supertype of all tuples.

val map = Map.empty[Int, Product]
map + (2 -> ("a", "b"))

And then to use the methods productArity, productElement and productIterator to handle the returned value.

You can also use a map of list (or any indexed collection).

val map = Map.empty[Int, List[_]]
map + (3 -> ("a" :: "b" :: "c" :: Nil))
map + (2 -> List("a", "b"))

The last solution is not that convenient for the user, but at least you know exactly what collection you handle. You could also add an implicit.

answered Dec 9, 2012 at 12:05

Lomig Mégard

1,83814 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Scala generic (tuple) type with multiple subtypes

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related