覆盖 Scala 集中的 toString [英] Override toString in a Scala set

问题描述

我想创建一组名为 IntSet 的整数.IntSet 在各方面都与 Set[Int] 相同，只是它的 toString 函数将元素打印为逗号分隔(就像你称为 mkString(","))，它有一个构造函数，它接受一个 Traversable 整数.最简单的方法是什么?

<代码>>IntSet((1 到 3)).toString1,2,3

我认为会有一些单行方式来做到这一点，但我一直在摆弄隐式函数并扩展 HashSet 并且我无法弄清楚.<小时>

诀窍是使用代理对象.Eastsun 在下面给出了答案.这是一个稍微不同的版本，它定义了一个命名的 IntSet 类型并使其不可变.

import collection.immutable.{HashSet, SetProxy}class IntSet(values: Traversable[Int]) extends SetProxy[Int] {覆盖 val self: Set[Int] = HashSet(values.toSeq:_*)覆盖 def toString() = mkString(",")}

解决方案

scala>导入 scala.collection.mutable导入 scala.collection.mutable标度>def IntSet(c: Traversable[Int]): mutable.Set[Int] = new mutable.SetProxy[Int] {|覆盖 val self: mutable.Set[Int] = mutable.HashSet(c.toSeq :_*)|覆盖 def toString = mkString(",")|}IntSet: (c: Traversable[Int])scala.collection.mutable.Set[Int]标度>IntSet(1 到 3)res0:scala.collection.mutable.Set[Int] = 1,2,3

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(",")
}

解决方案

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

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