Scala | unapplySeq() method

Last Updated : 08 Apr, 2019

The unapplySeq() method is an Extractor method. It extracts an Object of particular type and then again reconstructs it into a Sequence of extracted values and the length of this Sequence is not specified at the time of compilation. So, in order to reconstruct an Object that contains a Sequence, you need to utilize this unapplySeq method.
Syntax:

def unapplySeq(object: X): Option[Seq[T]]

Here, we have an object of type X and this method either returns None, when the object does not match or returns a Sequence of extracted values of type T, enclosed in class Some.
Now, lets understand it through some examples.

Example :

// Scala program of unapplySeq 
// method 
  
// Creating object 
object GfG 
{ 
  
    // Defining unapplySeq method 
    def unapplySeq(x:Any): Option[Product2[Int,Seq[String]]] = 
    { 
  
        val y = x.asInstanceOf[Author]  
          
        if(x.isInstanceOf[Author])  
        { 
            Some(y.age, y.name) 
        }      
        else
            None 
    }  
  
    // Main method 
    def main(args:Array[String]) = 
    { 
  
        // Creating object for Author 
        val x = new Author 
  
        // Applying Pattern matching 
        x match
        { 
            case GfG(y:Int,_,z:String) =>
  
            // Displays output 
            println("The age of "+z+" is: "+y) 
        } 
  
        // Assigning age and name 
        x.age = 22
        x.name = List("Rahul","Nisha") 
  
        // Again applying Pattern matching 
        x match
        {                              
            case GfG(y:Int,_,z:String) => 
      
            //Displays output 
            println("The age of "+z+" is: "+y) 
        } 
    } 
} 
  
// Creating class for author 
class Author 
{ 
  
    // Assigning age and name 
    var age: Int = 24
    var name: Seq[String] = List("Rohit","Nidhi") 
} 

Output:

The age of Nidhi is: 24
The age of Nisha is: 22

Here, we have used a trait Product2 in the Option in order to pass two arguments to it. Product2 is a Cartesian product of two elements.
Example :

// Scala program of using  
//'UnapplySeq' method of  
// Extractors 
  
// Creating object 
object GfG  
{ 
  
    // Main method 
    def main(args: Array[String])  
    { 
        object SortedSeq 
        { 
      
            // Defining unapply method 
            def unapplySeq(x: Seq[Int]) = 
            { 
                if (x == x.sortWith(_ < _))  
      
                { 
                    Some(x)  
                } 
                else None 
            } 
        } 
          
        // Creating a List                      
        val x = List(1,2,3,4,5)  
  
        // Applying pattern matching 
        x match 
        {  
            case SortedSeq(a, b, c, d,e) =>
  
        // Displays output 
        println(List(a, c, e)) 
        }  
    } 
} 