scale set

import scala.collection.mutable.Set //This package must be imported

    val mylist = Array("a1","b2","c3")

    var myset:Set[String] = Set()
    
    mylist.foreach(s=>{val as = s+"!"
      myset += as        //给set
      println(as)  
    })
    println("------------")
    myset.foreach(s=>println(s))
    println("------------")

print result:

a1!
b2!
c3!
------------
c3!
a1!
b2!
------------