在Scala中添加到条件中的集合

Question

I've written a visitor pattern and I'm matching an overridden subclass. I want to add the variable to the set value of the object and then return the modified object. How can I do that syntactically?

trait PropositionOrderer extends Visitor[Proposition]{
  var OurSet = SortedSet[Name] _
    override def variable = {
      _ match {
        case name => Variable(name)//SortedSet+(name).andThen(Variable(_))
      }
    }
}

Is there syntax to chain like a void function that adds to the SortedSet and then wait? I can't use andThen because I want to do two things, I want to add it to the Set and then I want to return the variable. Any ideas?

Answer 1

I think you mean something like this:

var ourSet = Set[String]()
def func(s: String) = 
  s match {
    case name =>        // a `case` can be followed by multiple statements 
      ourSet += name    // first we add `name` to the set
      name              // the last expression gets passed up to the assignment of x
  }
val x = func("test")
// ourSet is now Set("test")
// x is now "test"

A match expression will evaluate to the last expression of the matching case . Here, the case that matches is case name . The last expression under the case name block is name , so that's what the entire match evaluates to. So the function func returns name , which is "test" when we call func("test"). Thus, func("test"). Thus, x is assigned to be "test"`.

In addition, you can perform any other operations inside the case block you want. Here, we are modifying ourSet .