Scala pitfalls
1 like1,678 views
This document summarizes a presentation on Scala pitfalls. It discusses issues like overly complex one-liner code, null values, excessive use of Options, implicit conversions, and modularity problems with the cake pattern. It provides alternatives to consider like Subcut and MacWire. The presentation emphasizes keeping code clean and readable, using Options and implicits carefully, allowing for compiler and IDE limitations, and being mindful of compilation performance for large Scala projects.
![val
user:
Option[User]
=
???
if
(user
==
None)
{
//
foo!
}
else
{
//
bar!
val
u
=
user.get
}
Thursday, May 23, 13](https://image.slidesharecdn.com/scalapitfalls-130523013104-phpapp01/85/Scala-pitfalls-18-320.jpg)
![val
user:
Option[User]
=
???
if
(user.isDefined)
{
//
do
something
user-足full
}
else
{
//
oh
my,
what
now?
}
Thursday, May 23, 13](https://image.slidesharecdn.com/scalapitfalls-130523013104-phpapp01/85/Scala-pitfalls-19-320.jpg)
![val
user:
Option[User]
=
???
user
match
{
case
Some(u)
=>
//
now
I'm
happy!
case
None
=>
//
well,
doh
}
Thursday, May 23, 13](https://image.slidesharecdn.com/scalapitfalls-130523013104-phpapp01/85/Scala-pitfalls-20-320.jpg)
![Option monad
Option[T] ~= List of zero or one elements
Thursday, May 23, 13](https://image.slidesharecdn.com/scalapitfalls-130523013104-phpapp01/85/Scala-pitfalls-21-320.jpg)
![val
maybeUser:
Option[User]
=
???
maybeUser
map
{
user
=>
user.email
}
getOrElse
{
"foo@bar.com"
}
Thursday, May 23, 13](https://image.slidesharecdn.com/scalapitfalls-130523013104-phpapp01/85/Scala-pitfalls-22-320.jpg)
![val
maybeUser:
Option[User]
=
???
def
turnLeft(u:
User):
Option[User]
=
???
def
shake(u:
User):
Option[User]
=
???
def
shower(u:
User):
Option[User]
=
???
val
transformedUser:
Option[User]
=
maybeUser
.flatMap
(turnLeft)
.flatMap
(shake)
.flatMap
(shower)
Thursday, May 23, 13](https://image.slidesharecdn.com/scalapitfalls-130523013104-phpapp01/85/Scala-pitfalls-23-320.jpg)
Scala pitfalls
- 1. Scala pitfalls VSUG meetup 22.05.2013 Manuel Bernhardt - manuel@delving.eu - @elmanu Thursday, May 23, 13
- 4. Thursday, May 23, 13
- 5. Thursday, May 23, 13
- 6. Orders of ignorance 0th Order Ignorance: Lack of Ignorance 1st Order Ignorance: Lack of Knowledge 2nd Order Ignorance: Lack of Awareness 3rd Order Ignorance: Lack of a Suitably Ef鍖cient Process 4th Order Ignorance: Meta Ignorance Thursday, May 23, 13
- 7. Thursday, May 23, 13
- 8. One-liner of death Thursday, May 23, 13
- 9. BIG SCREEN I HAZ IT ! Thursday, May 23, 13
- 10. // update the thumbnail setThumbnaiL(id, USERCOLLECTION, collectionModel.thumbnail, findThumbnailUrl(collectionModel.thumbnail, collectionModel.objects), updatedUserCollection.links.filter(_.linkType == Link.LinkType.THUMBNAIL).map(_.link).headOption) Thursday, May 23, 13
- 11. // update the thumbnail setThumbnail(id, USERCOLLECTION, collectionModel.thumbnail, findThumbnailUrl(collectionModel.thumbnail, collectionModel.objects), updatedUserCollection.links.filter(_.linkType == Link.LinkType.THUMBNAIL).map(_.link).headOption) Thursday, May 23, 13
- 12. hard to read hidden context switching debugging? Thursday, May 23, 13
- 13. // update the thumbnail val thumbnailUrl = findThumbnailUrl( collectionModel.thumbnail, collectionModel.objects ) val maybeThumbnailLink = updatedUserCollection.links .filter(_.linkType == Link.LinkType.THUMBNAIL) .map(_.link) .headOption setThumbnail( id, USERCOLLECTION, collectionModel.thumbnail, thumbnailUrl, maybeThumbnailLink ) Thursday, May 23, 13
- 14. Scala Style guide Tools! Scalastyle, Scalariform Thursday, May 23, 13
- 15. null Thursday, May 23, 13
- 16. null Thursday, May 23, 13
- 17. So many Options Thursday, May 23, 13
- 18. val user: Option[User] = ??? if (user == None) { // foo! } else { // bar! val u = user.get } Thursday, May 23, 13
- 19. val user: Option[User] = ??? if (user.isDefined) { // do something user-足full } else { // oh my, what now? } Thursday, May 23, 13
- 20. val user: Option[User] = ??? user match { case Some(u) => // now I'm happy! case None => // well, doh } Thursday, May 23, 13
- 21. Option monad Option[T] ~= List of zero or one elements Thursday, May 23, 13
- 22. val maybeUser: Option[User] = ??? maybeUser map { user => user.email } getOrElse { "foo@bar.com" } Thursday, May 23, 13
- 23. val maybeUser: Option[User] = ??? def turnLeft(u: User): Option[User] = ??? def shake(u: User): Option[User] = ??? def shower(u: User): Option[User] = ??? val transformedUser: Option[User] = maybeUser .flatMap (turnLeft) .flatMap (shake) .flatMap (shower) Thursday, May 23, 13
- 24. Did you say implicit? Thursday, May 23, 13
- 25. implicit def string2Int(s: String): Int = Integer.parseInt(s) Thursday, May 23, 13
- 26. implicit def string2Int(s: String): Int = Integer.parseInt(s) val foo = "22" val bar = "some" def fooBar(i: Int) = i + 1 fooBar(foo) fooBar(bar) // ouch Thursday, May 23, 13
- 27. Its all about design Thursday, May 23, 13
- 28. use implicit conversions wisely: speci鍖c types use within the correct scope implicit lookup scope Thursday, May 23, 13
- 29. A word on IDEs Thursday, May 23, 13
- 30. Thursday, May 23, 13
- 31. Scala is complex IDEs are getting there, but are not there yet False negatives be especially misleading at the beginning Thursday, May 23, 13
- 32. Modularity Thursday, May 23, 13
- 33. Thursday, May 23, 13
- 34. Cake pattern pitfalls Initialization order Initialization order Compilation time overhead (traits) Beautiful theory, less beautiful practice Thursday, May 23, 13
- 35. Cake pattern pitfalls Initialization order Initialization order Compilation time overhead (traits) Beautiful theory, less beautiful practice WAT? Thursday, May 23, 13
- 36. Alternatives Subcut MacWire - macros! Guice, Spring Scala Thursday, May 23, 13
- 37. Time is money Thursday, May 23, 13
- 39. Scala compilation is slow Incremental compilation about to get better Get appropriate hardware Thursday, May 23, 13
- 40. Useful links Scala style guide - http://docs.scala-lang.org/style/ Scalastyle - http://www.scalastyle.org SBT-scalariform: https://github.com/sbt/sbt-scalariform Post on implicits - http://stackover鍖ow.com/questions/5598085/where-does-scala-look-for- implicits Cake pattern - http://jonasboner.com/2008/10/06/real-world-scala-dependency-injection-di/ Subcut - https://github.com/dickwall/subcut MacWire - https://github.com/adamw/macwire Play 2.1 MacWire demo - https://github.com/przemek-pokrywka/play-2.1-macwire-demo Orders of ignorance - http://www-plan.cs.colorado.edu/diwan/3308-s10/p17-armour.pdf Thursday, May 23, 13
- 41. Questions? @elmanu manuel@delving.eu http://github.com/manuelbernhardt Thursday, May 23, 13