Pattern Matching

It is a generalization of C or Java’s switch statement. In this match method is used instead switch statement. It is defined in Scala’s root class Any and therefore is available for all objects. The match method takes a number of cases as an argument. Each alternative takes a pattern and one or more expressions which will be performed if the pattern matches. A symbol => is used to separate the pattern from the expressions.

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e.g.

object Intellipaat {
def main(args: Array[String]) {
println(matchValue(2))
}
def matchValue(i: Int): String = i match {
case 1 => "one"
case 2 => "two"
case 3=> "three"
case _=> "unknown"
}
}

Output
two
If patterns are of different type in different cases the use Any except Int and String in above example.
Case Classes
These are the special types of classes which are used for pattern matching with case expressions. By adding case keyword there are number of advantages which are:

  • Compiler automatically changes the constructor arguments into immutable fields.
  • Compiler automatically includes equals, hashCode and toString methods to the class


Syntax

case class Calculator(Value: Type)

e.g.

object Intellipaat {
def main(args: Array[String]) {
val a = new employee(1, “abc”)
val b  = new employee(2, “xyz”)
val c  = new employee(3, “pgr”)
for (employee <- List(a, b, c)) {
employee match {
case employee(1, “abc”) => println("Hello abc")
case employee(2, “xyz”) => println(“Hello xyz”)
case employee(id, employee_name) => println("ID: " +id + ", Employee:" + employee_name)
}
}
}
case class employee(id: Int, employee_name: String) // case class
}

Output
Hello abc
Hello xyz
ID: 3, Employee: pqr

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