Refactoring Design Patterns the Functional Way (in Scala)

@kfirondev
Refactoring Design Patterns the
Functional Way (in Scala)
@kfirondev
Kfir Bloch
Backend engineering manager

@kfirondev
What the hell is
functional programming?

@kfirondev
• Treats computation as the evaluation of
mathematical functions
• Avoid changing state and mutable data
• Declarative
• Pure functions with no side effects
http://www.clker.com/

@kfirondev
case class Salad(name: String,
veggy: Boolean,
chopped: Boolean)
Immutability via
Scala case class

@kfirondev
sealed trait Salad
case class Lentils() extends Salad
case class Hummus() extends Salad
case class Tahini() extends Salad
case class SaladInfo(salad: Salad, spices: Seq[String])
def makeSaladInfo(salad: Salad,
f: Salad => Seq[String]): SaladInfo =
SaladInfo(salad, f(salad))
// usage
makeSaladInfo(Hummus(), spicer)
def spicer(salad: AnyRef): Seq[String] =
salad match {
case l: Lentils => Seq("Salt", "Olive Oil", "Red paper")
case h: Hummus => Seq("Salt", "Garlic", "Onion")
case t: Tahini => Seq("Salt", "Garlic", "Lemon")
}
Higher order
function

@kfirondev
def doSomething(msg: String): Unit= {
val formatted = msg.toUpperCase
logger.log(Level.WARNING, formatted)
}
Function with side
effects

@kfirondev
def doSomething(msg: String): String = {
val formatted = msg.toUpperCase
formatted
}
Pure function

@kfirondev
It leads
naturally to
Hexagonal
Architecture
(ports & adapters)
http://blog.mattwynne.net/2012/05/31/hexagonal-rails-objects-values-and-hexagons/comment-
page-1/

@kfirondev
Hexagonal Architecture with FP
gives result which is:
Deterministic Separation of concerns Fast testing lifecycle Concurrent agnostic
domain model

@kfirondev
People told you that ->

@kfirondev
Abstract factory
Builder
Factory Method
Builder
Prototype
Adapter
Bridge
Composite
Decorator
Proxy
Chain of
responsibility
Command
Iterator
Mediator
Observer
Object Oriented

@kfirondev
Abstract factory
Builder
Factory Method
Builder
Prototype
Adapter
Bridge
Composite
Decorator
Proxy
Chain of
responsibility
Command
Iterator
Mediator
Observer
Object Oriented
Functional
Programming

@kfirondev
Builder pattern builds a complex object using
simple objects and using a step by step
approach. This type of design pattern comes
under creational pattern as this pattern
provides one of the best ways to create an
object.
Builder

@kfirondev
Builder pattern builds a complex object using
simple objects and using a step by step
approach. This type of design pattern comes
under creational pattern as this pattern
provides one of the best ways to create an
object.
Builder
LET’S
CODE

@kfirondev
Behavior pattern that helps create objects
which represent various strategies and a
context object whose behavior varies as per
its strategy object. The strategy object
changes the executing algorithm of the context
object
Strategy

@kfirondev
LET’S
CODE
Behavior pattern that helps create objects
which represent various strategies and a
context object whose behavior varies as per
its strategy object. The strategy object
changes the executing algorithm of the context
object
Strategy

@kfirondev
The chain-of-responsibility pattern is a design pattern
consisting of a source of command objects and a series
of processing objects.
Each processing object contains logic that defines the
types of command objects that it can handle.
Only qualifying predicate for the request will process it,
otherwise it will pass to the next handler in chain
Chain of
Responsibility

@kfirondev
LET’S
CODE
The chain-of-responsibility pattern is a design pattern
consisting of a source of command objects and a series
of processing objects.
Each processing object contains logic that defines the
types of command objects that it can handle.
Only qualifying predicate for the request will process it,
otherwise it will pass to the next handler in chain
Chain of
Responsibility

@kfirondev
In software engineering, dependency injection is a
software design pattern that implements inversion of
control for resolving dependencies. A dependency is an
object that can be used (a service)
Dependency
Injection

@kfirondev
In software engineering, dependency injection is a
software design pattern that implements inversion of
control for resolving dependencies. A dependency is an
object that can be used (a service)
Dependency
Injection
Dependency Injection framework
!=
Dependency Injection

@kfirondev
Dependency injection
SpringEJB Guice
Dependency Injection Frameworks

@kfirondev
SpringEJB Guice
Constructor
Injection
Vanilla

@kfirondev
SpringEJB Guice
Cake
Pattern
Constructor
Injection
Vanilla

@kfirondev
SpringEJB Guice
Cake
Pattern
Constructor
Injection
Vanilla
LET’S
CODE

@kfirondev
• https://github.com/kfiron/design-pattern-
fp-talk
My code is available for you

@kfirondev
• Went over functional programming definition
• Understood that FP as “side effect” help you go
towards hexagonal architecture
• Refactor various patterns from Java to Scala
Idioms
• Dependency injection using Scala with cake
pattern
Summary of what we did

@kfirondev
linkedin/in/blochkfir github.com/kfiron@kfirondevkfirb@wix.com
Kfir Bloch
Head of Backend Engineering
Q&A

@kfirondev
Thank YouWix Engineering Blog
http://engineering.wix.com/
We are hiring
http://jobs.wix.com
email
jobs@wix.com
@kfirondev
Kfir Bloch

Refactoring Design Patterns the Functional Way (in Scala)

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