Scala Stack ++:() method with example

In Scala, scala.collection.mutable implements Stack data structure. The ++: method is similar to ++ method in Stack which gives a new stack with elements from the left hand operand followed by the elements from the right hand operand. But with the difference that in ++:() right operand determines the type of the resulting collection rather than the left one.

Method Definition – def ++:[B >: A, That](that: collection.Traversable[B])

Returns – A new stack which contains all elements of this stack followed by all elements of traversable.

Example #1:

// Scala program of mutable stack ++:() method

// Import Stack
import scala.collection.mutable._

// Creating object
object GfG
{

    // Main method
    def main(args:Array[String])
    {
        // Creating a stack
        val q1 = Stack(1, 2, 3, 4, 5)

        val q2 = Stack(11, 12, 13, 14, 15)

        // Applying ++() method
        val result = q1.++:(q2)

        // Display output
        print(result)

    }
}

Output:

Stack(11, 12, 13, 14, 15, 1, 2, 3, 4, 5)

Example #2:

// Scala program of mutable stack ++()
// method

// Import Stack
import scala.collection.mutable._

// Creating object
object GfG
{

    // Main method
    def main(args:Array[String])
    {
        // Creating a stack
        val q1 = List(1, 2, 3)

        val q2 = Stack("for", "geeks")

        // Applying ++() method
        val result = q1 ++: q2

        // Display output
        print(result)

    }
}

Output:

Stack(1, 2, 3, for, geeks)