refactoring design patterns the functional way (in scala)
TRANSCRIPT
@kfirondev
Refactoring Design Patterns the Functional Way (in Scala)
@kfirondev
Kfir BlochBackend 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
People told you that ->
Abstract factory
Builder
Factory Method
Builder
Prototype
Adapter
Bridge
Composite
Decorator
Proxy
Chain of responsibility
Command
Iterator
Mediator
Observer
Object Oriented
http://www.clker.com/
@kfirondev
People told you that ->
Abstract factory
Builder
Factory Method
Builder
Prototype
Adapter
Bridge
Composite
Decorator
Proxy
Chain of responsibility
Command
Iterator
Mediator
Observer
Object Oriented FunctionalProgramming
http://www.clker.com/
@kfirondev
People told you that ->
Abstract factory
Builder
Factory Method
Builder
Prototype
Adapter
Bridge
Composite
Decorator
Proxy
Chain of responsibility
Command
Iterator
Mediator
Observer
Object Oriented FunctionalProgramming
http://www.clker.com/
Incorrect!
@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 ofResponsibility
@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 ofResponsibility
@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)
DependencyInjection
@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)
DependencyInjection
Dependency Injection framework!=
Dependency Injection
@kfirondev
Dependency injection
SpringEJB Guice
Dependency Injection Frameworks
@kfirondev
Dependency injection
SpringEJB Guice
Dependency Injection Frameworks
Constructor Injection
Vanilla
@kfirondev
Dependency injection
SpringEJB Guice
Dependency Injection Frameworks
CakePattern
Constructor Injection
Vanilla
@kfirondev
Dependency injection
SpringEJB Guice
Dependency Injection Frameworks
CakePattern
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@kfirondev
@kfirondev
linkedin/in/blochkfir github.com/kfiron@[email protected]
Kfir BlochHead of Backend Engineering
Q&A
@kfirondev
Thank You Wix Engineering Blog
http://engineering.wix.com/
We are hiring http://jobs.wix.com
@kfirondev
Kfir Bloch