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Prasanna Kumar

Structural (or) Type Safe Duck Typing in Scala

Structural typing as defined by Wikipedia

“A structural type system (or property-based type system) is a major classof type system, in which type compatibility and equivalence are determined by the type’s structure, and not by other characteristics such as its name or place of declaration “

Strutural types in scala allows code modularity for some specific situations.For instance, if a behaviour is implemented across several classes and those behaviours need to invoked by the structure of the type. This approach rules out the need for an abstract class or trait merely for the purpose of calling single overridden method. Structural typing not onlyadds syntatic sugar but also makes the code much modular.

Lets consider a behaviour ‘walk’ in classes Cat and Dog. The StrucType class’s whoIsWalking takes a type param which states that “Accept any object which has a method walk and that returns a string” type is aliazed with a variable ‘c’ and with in the method the aliazed variable can invoke ‘walk’.

class StrucType {
  def whoIsWalking(c:{def walk():String}) = println(c.walk)

Below are the classes which has the method commons.class

class Cat {
  def walk():String = 'Cat walking'

class Dog {
  def walk():String = 'Dog walking'
 * object Main {
    def main(args:Array[String]) {

    println('Hello Scala')

    val walkerStruct = new StrucType();

    walkerStruct.whoIsWalking(new Cat());

    walkerStruct.whoIsWalking(new Dog());

Structural typing can also be considered to refactor your next strategy pattern implementation. Iam planning to explain about them in my next post stay tuned !!!!!

Reference: Structural (or) Type Safe Duck Typing in Scala from our JCG partner Prasanna Kumar at the Prassee on Scala blog.

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