Scala Refactoring for Fun and Profit
Download as PPTX, PDF5 likes989 views
This document discusses refactoring Scala code to improve quality and maintainability. It provides examples of issues like stringly typed code, abuse of collections, and poor scoping. The presentation recommends addressing these by using case classes instead of tuples, parsing values instead of passing raw strings, giving intermediate steps meaningful names, and separating logic and data through traits or type classes. Well-scoped code with a small public API and private implementation details is emphasized.
 = a.success[List[String]]
val add3 = (x: Int) =>
(y: Int) =>
(z: Int) => x + y + z
val res = (7) <*> (s(8) <*> (s(9) ∘ add3))
assert(res == s(24))](https://image.slidesharecdn.com/codemotion2015-scalarefactoringforfunandprofit-151217160330/85/Scala-Refactoring-for-Fun-and-Profit-10-320.jpg)
![Stringly Typed
• Examples:
– Passing dates as strings
– Carrying unparsed data around
– Using empty strings instead of Options
case class Person(name: String, location: String)
def nearest(to: Person, all: List[Person]): Person = {
val geo: Point = Point.parse(to.location)
all.minBy(p => geo.distanceTo(Point.parse(p.location)))
}
1. Inefficient (space/time)
2. Error handling all over the place
3. What’s with all the boilerplate?](https://image.slidesharecdn.com/codemotion2015-scalarefactoringforfunandprofit-151217160330/85/Scala-Refactoring-for-Fun-and-Profit-15-320.jpg)
![Stringly Typed
• Examples:
– Passing dates as strings
– Carrying unparsed data around
– Using empty strings instead of Options
case class Person(name: String, location: Point)
def nearest(to: Person, all: List[Person]): Person =
all.minBy(p => to.location distanceTo p.location)1. Efficient (only parsed once)
2. Sane error handling
3. Zero boilerplate!](https://image.slidesharecdn.com/codemotion2015-scalarefactoringforfunandprofit-151217160330/85/Scala-Refactoring-for-Fun-and-Profit-16-320.jpg)
![Collective Abuse
• Common anti-patterns:
– Too many inline steps
– Tuple overload
val actors: List[(Int, String, Double)] = // ...
def bestActor(query: String) =
actors.filter(_._2 contains query)
.sortBy(-_._3)
.map(_._1)
.headOption
1. What does this even do?!
2. How does data flow here?](https://image.slidesharecdn.com/codemotion2015-scalarefactoringforfunandprofit-151217160330/85/Scala-Refactoring-for-Fun-and-Profit-20-320.jpg)
![Collective Abuse
• Common anti-patterns:
– Too many inline steps
– Tuple overload
val actors: List[(Int, String, Double)] = // ...
def bestActor(query: String) = {
val matching = actors.filter(_._2 contains query)
val bestByScore = matching.sortBy(-_._3).headOption
bestByScore.map(_._1)
} Name intermediate steps!](https://image.slidesharecdn.com/codemotion2015-scalarefactoringforfunandprofit-151217160330/85/Scala-Refactoring-for-Fun-and-Profit-21-320.jpg)
![Collective Abuse
• Common anti-patterns:
– Too many inline steps
– Tuple overload
val actors: List[(Int, String, Double)] = // ...
def bestActor(query: String) =
actors.filter(_._2 contains query)
.sortBy(-_._3)
.map(_._1)
.headOption
What’s with all these
underscores?](https://image.slidesharecdn.com/codemotion2015-scalarefactoringforfunandprofit-151217160330/85/Scala-Refactoring-for-Fun-and-Profit-22-320.jpg)
![Collective Abuse
• Common anti-patterns:
– Too many inline steps
– Tuple overload
case class Actor(id: Int, name: String, score: Double)
def bestActor(query: String, actors: List[Actor]) =
actors.filter(_.name contains query)
.sortBy(-_.score)
.map(_.id)
.headOption
Scala classes are cheap.
Use them.](https://image.slidesharecdn.com/codemotion2015-scalarefactoringforfunandprofit-151217160330/85/Scala-Refactoring-for-Fun-and-Profit-23-320.jpg)
Scala Refactoring for Fun and Profit
- 1. Scala Refactoring Tomer Gabel, CodeMotion Tel-Aviv 2015 for Fun and Profit
- 2. Agenda • For the next 40 minutes, we’ll: – Look at examples – Discuss patterns – … and anti-patterns – Showcase refactoring techniques
- 3. Our Victim • … is ScalaChess – Provides a full domain model for chess – Good test coverage – Long-lived – High quality code – MIT license – Integrated in lichess.org * ScalaChess is an open-source project by Thibault Duplessis
- 4. STARTING OFF
- 5. Naming Things • New features complicate matters: – Infix notation (a.k.a dot-free syntax) case class Geo(lat: Double, long: Double) { def distance(other: Geo): Double = // ... } val (center, location): Geo = // ... if (centre.distance(location) <= radius) Some(loc) else None
- 6. Naming Things • New features complicate matters: – Infix notation (a.k.a dot-free syntax) case class Geo(lat: Double, long: Double) { def distance(other: Geo): Double = // ... } val (center, location): Geo = // ... if (centre distance location <= radius) Some(loc) else None What language is this?
- 7. Naming Things • New features complicate matters: – Infix notation (a.k.a dot-free syntax) case class Geo(lat: Double, long: Double) { def distanceFrom(other: Geo): Double = //… } val (center, location): Geo = // ... if (location distanceFrom center <= radius) Some(loc) else None A little clearer now
- 8. Naming Things • Oh, the humanity: Symbolic operators case class Geo(lat: Double, long: Double) { def <->(other: Geo): Double = // ... } val Geo(center, location) = // ... if (loc <-> center <= radius) Some(loc) else None Why would you do that?!
- 9. Naming Things • There are worse offenders. Take Dispatch: import dispatch.Http import Http._ val server = url("http://example.com") val headers = Map("Accept" -> "application/json") Http(server >>> System.out) // GET Http(server <:< headers >>> System.out) // GET Http(server << yourPostData >|) // POST
- 10. Naming Things • There are worse offenders. Take scalaz: def s[A](a: A) = a.success[List[String]] val add3 = (x: Int) => (y: Int) => (z: Int) => x + y + z val res = (7) <*> (s(8) <*> (s(9) ∘ add3)) assert(res == s(24))
- 12. THE LAY OF THE LAND
- 13. Stringly Typed “Used to describe an implementation that needlessly relies on strings when programmer & refactor friendly options are available.” -- Coding Horror
- 14. Stringly Typed • Examples: – Passing dates as strings – Carrying unparsed data around – Using empty strings instead of Options case class Person(name: String, created: String) def resolveConflict(p1: Person, p2: Person): Person = { val c1 = dateParser.parse(p1.created) val c2 = dateParser.parse(p2.created) if (c1 compareTo c2 > 0) p1 else p2 } 1. Parser needs to be well-known 2. Error handling all over the place 3. What’s with all the boilerplate?
- 15. Stringly Typed • Examples: – Passing dates as strings – Carrying unparsed data around – Using empty strings instead of Options case class Person(name: String, location: String) def nearest(to: Person, all: List[Person]): Person = { val geo: Point = Point.parse(to.location) all.minBy(p => geo.distanceTo(Point.parse(p.location))) } 1. Inefficient (space/time) 2. Error handling all over the place 3. What’s with all the boilerplate?
- 16. Stringly Typed • Examples: – Passing dates as strings – Carrying unparsed data around – Using empty strings instead of Options case class Person(name: String, location: Point) def nearest(to: Person, all: List[Person]): Person = all.minBy(p => to.location distanceTo p.location)1. Efficient (only parsed once) 2. Sane error handling 3. Zero boilerplate!
- 17. Stringly Typed • Examples: – Passing dates as strings – Carrying unparsed data around – Using empty strings instead of Options case class Person(firstName: String, lastName: String) def render(p: Person): String = s""" |<div id='first-name'>${p.firstName}</div> |<div id='last-name'>${p.lastName}</div> """.stripMargin 1. Nothing enforces emptiness check! 2. Scala has a great type for these :-)
- 19. Collective Abuse • Scala has a massive collection library • Loads of built-ins too – Case classes – Functions and partials – Tuples, tuples, tuples • Fairly easy to abuse
- 20. Collective Abuse • Common anti-patterns: – Too many inline steps – Tuple overload val actors: List[(Int, String, Double)] = // ... def bestActor(query: String) = actors.filter(_._2 contains query) .sortBy(-_._3) .map(_._1) .headOption 1. What does this even do?! 2. How does data flow here?
- 21. Collective Abuse • Common anti-patterns: – Too many inline steps – Tuple overload val actors: List[(Int, String, Double)] = // ... def bestActor(query: String) = { val matching = actors.filter(_._2 contains query) val bestByScore = matching.sortBy(-_._3).headOption bestByScore.map(_._1) } Name intermediate steps!
- 22. Collective Abuse • Common anti-patterns: – Too many inline steps – Tuple overload val actors: List[(Int, String, Double)] = // ... def bestActor(query: String) = actors.filter(_._2 contains query) .sortBy(-_._3) .map(_._1) .headOption What’s with all these underscores?
- 23. Collective Abuse • Common anti-patterns: – Too many inline steps – Tuple overload case class Actor(id: Int, name: String, score: Double) def bestActor(query: String, actors: List[Actor]) = actors.filter(_.name contains query) .sortBy(-_.score) .map(_.id) .headOption Scala classes are cheap. Use them.
- 25. Scoping • Correct scoping is incredibly important! –Separation of concerns –Code navigation and discovery –Reduced autocompletion noise
- 26. Scoping • Scala offers an impressive toolbox: – Nested scopes – Companion objects – Traits – Visibility modifiers – Type classes
- 27. Scoping class User(var name: String, var age: Int, initialStatus: UserStatus = New) { private var _status = initialStatus def status = _status def delete(): Unit = { _status = Deleted Mailer.notify(Mailer.userDeletion, this) } } Mutable data ⇒ Boilerplate SoC broken!
- 29. Scoping • Lessons learned: –Keep logic and data separate –Case classes are your friends! –Add “aspects” via type classes
- 30. Scoping • Rules of the road: –Keep your public API small –Make everything else private –Put helpers in companions –… or via implicit extensions
Editor's Notes
- #10: Source: http://stackoverflow.com/questions/5564074/scala-http-operations
- #11: Source: http://scalaz.github.io/scalaz/scalaz-2.9.1-6.0.4/doc.sxr/scalaz/example/ExampleApplicative.scala.html
- #12: Photo source: https://flic.kr/p/3xcrQG
- #13: Image source: http://www.flickeringmyth.com/2015/06/fallout-4-graphics-and-why-visual-demands-are-dumb.html
- #19: Image source: https://thisistwitchy.files.wordpress.com/2013/04/oh-the-horror.jpg
- #20: Image source: http://onlinesalesstepbystep.com/wp-content/uploads/2014/08/Toppling-books.jpg
- #25: Photo source: https://flic.kr/p/3xcrQG
- #27: Photo source: https://flic.kr/p/c4QJzC
- #29: Photo source: https://flic.kr/p/3xcrQG