5-pattern-matching.md

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Pattern Matching	Think “switch” on steroids. Match against class hierarchies, sequences, constants and more.

Switch on the structure of your data

In Scala, case classes are used to represent structural data types. They implicitly equip the class with meaningful toString, equals and hashCode methods, as well as the ability to be deconstructed with pattern matching.

In this example, we define a small set of case classes that represent binary trees of integers (the generic version is omitted for simplicity here). In inOrder, the match construct chooses the right branch, depending on the type of t, and at the same time deconstructs the arguments of a Node.

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                                    <div class="bar-code"><span>Pattern matching</span></div>
                                    <pre><code>// Define a set of case classes for representing binary trees.

sealed abstract class Tree case class Node(elem: Int, left: Tree, right: Tree) extends Tree case object Leaf extends Tree

// Return the in-order traversal sequence of a given tree. def inOrder(t: Tree): List[Int] = t match { case Node(e, l, r) => inOrder(l) ::: List(e) ::: inOrder(r) case Leaf => List() }

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