CODESAMPLE

Specification - Scala

Specification Scala

The Specification pattern is a way to define complex business rules or constraints as objects. These objects encapsulate the logic for checking if a given data object meets the criteria. This promotes reusability, composability, and testability of rules.

The Scala code defines a Specification trait with a isSatisfiedBy method. Concrete specifications are created by extending this trait and implementing the isSatisfiedBy method to define the specific rule. The example demonstrates combining specifications using and and or to create more complex rules. Scala’s functional nature and support for traits make it a natural fit for this pattern, allowing for concise and composable rule definitions. Immutability is also leveraged for thread safety and predictable behavior.

trait Specification[T] {
  def isSatisfiedBy(item: T): Boolean

  def and(other: Specification[T]): Specification[T] =
    new Specification[T] {
      def isSatisfiedBy(item: T): Boolean =
        Specification.this.isSatisfiedBy(item) && other.isSatisfiedBy(item)
    }

  def or(other: Specification[T]): Specification[T] =
    new Specification[T] {
      def isSatisfiedBy(item: T): Boolean =
        Specification.this.isSatisfiedBy(item) || other.isSatisfiedBy(item)
    }
}

case class Person(age: Int, name: String)

object SpecificationExamples {
  def main(args: Array[String]): Unit = {
    val adult = new Specification[Person] {
      def isSatisfiedBy(person: Person): Boolean = person.age >= 18
    }

    val namedBob = new Specification[Person] {
      def isSatisfiedBy(person: Person): Boolean = person.name == "Bob"
    }

    val bobAndAdult = adult and namedBob
    val person1 = Person(20, "Bob")
    val person2 = Person(15, "Bob")
    val person3 = Person(20, "Alice")

    println(s"Person 1 satisfies adult and Bob: ${bobAndAdult.isSatisfiedBy(person1)}") // true
    println(s"Person 2 satisfies adult and Bob: ${bobAndAdult.isSatisfiedBy(person2)}") // false
    println(s"Person 3 satisfies adult and Bob: ${bobAndAdult.isSatisfiedBy(person3)}") // false

    val adultOrBob = adult or namedBob
    println(s"Person 1 satisfies adult or Bob: ${adultOrBob.isSatisfiedBy(person1)}") // true
    println(s"Person 2 satisfies adult or Bob: ${adultOrBob.isSatisfiedBy(person2)}") // true
    println(s"Person 3 satisfies adult or Bob: ${adultOrBob.isSatisfiedBy(person3)}") // true
  }
}