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Scala Extractors

By IncludeHelp Last updated : October 28, 2024

What is an Extractor in Scala

An extractor is a special type of object that has some special methods. These methods are: apply() and unapply().

• The apply() method of extractor object is used to feeding values for the object, it takes parameter values, formats them and adds them to the object.
• The unapply() method of extractor object is used to delete values from the object, it matches the value and removes them from the object list.

Working of Extractors

Let's take an example of an object that apply() as well as unapply() method. The apply() method takes arguments and adds them to class. The unapply() does the exact opposite, it takes arguments, matches them and then deletes, i.e. deconstructs.

Example of Scala Extractor

The following is an example of Scala extractor using apply and unapply methods in Scala's Student object:

object Student {
  def main(args: Array[String]): Unit = {
    def apply(name: String, result: String): String = {
      name + " is " + result
    }

    def unapply(x: String): Option[(String, String)] = {
      val y = x.split(" is ")
      if (y.length == 2 && y(1) == "Pass") {
        Some(y(0), y(1))
      } else {
        None
      }
    }

    println("The Apply method returns: " + apply("Ram", "Pass"))
    println("The Unapply method returns: " + unapply("Ram is Pass").getOrElse("No match"))
  }
}

Output

The Apply method returns : Ram is Pass
The Unapply method returns : Some((Ram,Pass))

Explanation

The unapply() method here, checking if the student is passed and removes it based on the result.