Override toString in a Scala set

scala, scala-collections, tostring

Solution

scala> import scala.collection.mutable
import scala.collection.mutable

scala> def IntSet(c: Traversable[Int]): mutable.Set[Int] = new mutable.SetProxy[Int] {
     |   override val self: mutable.Set[Int] = mutable.HashSet(c.toSeq :_*)
     |   override def toString = mkString(",")
     | }
IntSet: (c: Traversable[Int])scala.collection.mutable.Set[Int]

scala> IntSet(1 to 3)
res0: scala.collection.mutable.Set[Int] = 1,2,3

Problem

I want to create a set of integers called `IntSet`. `IntSet` is identical to `Set[Int]` in every way except that its `toString` function prints the elements as comma-delimited (the same as if you called `mkString(",")`), and it has a constructor that takes a `Traversable` of integers. What is the simplest way to do this? ``` > IntSet((1 to 3)).toString 1,2,3 ``` I'd think there would be some one-line way to do this, but I've been fiddling around with implicit functions and extending `HashSet` and I can't figure it out. The trick is to use a proxy object. Eastsun has the answer below. Here's a slightly different version that defines a named `IntSet` type and makes it immutable. ``` import collection.immutable.{HashSet, SetProxy} class IntSet(values: Traversable[Int]) extends SetProxy[Int] { override val self: Set[Int] = HashSet(values.toSeq:_*) override def toString() = mkString(",") } ```

Original source