Scala：设置可更新集合的操作吗？

Question

I am looking at the mutable Set class and see union , intersect , diff , etc. All of these set operations create a new Set . I was curious if there is a way to update the Set rather than create a new one. Otherwise, I have to switch from val to var or I have to follow up with additional steps.

In case I'm not being clear, consider .NET's HashSet class. It has IntersectWith , ExceptWith and UnionWith that modify the collection. Whereas the LINQ extension methods Intersect , Except and Union create new collections. I'm hoping to find something equivalent to the "With" variants.

Here's an inefficient approach that rebuilds the collection from scratch:

val temp = original.diff(other)
original.clear()
original ++= temp

Obviously, it would be more efficient to do this:

for (value <- other if original.contains(value)) {
    original.remove(value)
}

Answer 1

See: http://docs.scala-lang.org/overviews/collections/sets.html#operations-in-class-mutableset

For example:

Additions: xs += x Adds element x to set xs as a side effect and returns xs itself.

So just ignore the returned value. The set should be updated in-place.