Dependency injection in Scala: Constructors and cakes

A look at two methods of dependency injection in Scala. DIY approach with constructor injection and the cake pattern.

Transcript

1. Dependency  injec+on  in  Scala   Constructors and Cakes javaBin, Trondheim – 2.11.2011
2. Constructor  injec+on   Cake  pa6ern   (Guice,  Spring  etc)  
3. Constructor  injec+on   new SomeClass(dep1, dep2)
4. new SomeClass(dep1, dep2) +   Constructor  injec+on  
5. Constructor  injec+on   new SomeClass(dep1, dep2) +   ÷  
6. Cake  pa6ern  
7. Cake  pa6ern   (mmmm,  cake)  
8. Complete   compile  +me  verifica+on  
9. Prerequisites  
10. Abstract  (type)  members   trait SomeComponent { type T <: SomeInterface def methodThing: SomeInterface val aThing: SomeInterface trait SomeInterface { // Stuff } }  
11. Self  type  annota+ons   trait AnotherComponentImpl extends AnotherComponent { this: SomeComponent => val aThing = new SomeInterfaceImpl class AnotherInterfaceImpl extends AnotherInterface { // Impl stuff } }  
12. Modular  mixin  composi+on   object ComponentRegistry extends SomeComponentImpl with AnotherComponentImpl ... val myThing = ComponentRegistry.aThing new SomeComponentImpl with AnotherComponent { val aThing = new FavouriteImpl(‘a parameter’) }  
13. Modular  mixin  composi+on   trait TestComponentRegistry extends SomeComponentImpl with AnotherComponentImpl with org.specs.mock.JMocker { val aThing = mock(classof[SomeInterface]) }
14. trait SomeComponent { val aThing: SomeInterface trait SomeInterface { // Stuff } } trait AnotherComponentImpl extends AnotherComponent { this: SomeComponent => def myMethod { aThing.usefulStuff() } }   object ComponentRegistry extends AnotherComponentImpl with SomeComponentImpl { val aThing = new MyFavouriteImpl }
15. A  whole  cake   and  nothing  but  the  cake  
16. All  is  well,  except…   …but  s+ll  cool,  me  thinks  
17. What’s  next?  
18. Credits   •  “Dependency  Injec+on  Op+ons  in  Scala”  –  Dick  Wall  @  JavaZone  X  2011   –  h6p://vimeo.com/28792660   •  “Scalable  Component  Abstrac+ons”  –  Mar+n  Odersky,  Ma6hias  Zenger   –  h6p://lamp.epfl.ch/~odersky/papers/ScalableComponent.pdf   •  “Real-­‐World  Scala:  Dependency  Injec+on  (DI)”  –  Jonas  Bonér   –  h6p://jonasboner.com/2008/10/06/real-­‐world-­‐scala-­‐dependency-­‐injec+on-­‐ di.html   •  “Do  it  Yourself  –  Dependency  Injec+on”  –  Miško  Hevery/Chad  Parry   –  h6p://misko.hevery.com/2010/05/26/do-­‐it-­‐yourself-­‐dependency-­‐injec+on/   •  “Slicing  the  cake”  –  Przemek  Pokrywka   –  h6p://biased-­‐and-­‐fair-­‐solware-­‐development.blogspot.com/2011/01/slicing-­‐ cake.html   •  “Dependency  Injec+on  in  Scala:  Extending  the  Cake  Pa6ern”  –  Adam  Warski   –  h6p://www.warski.org/blog/2010/12/di-­‐in-­‐scala-­‐cake-­‐pa6ern/   •  “DI  in  Scala:  Cake  Pa6ern  pros  &  cons”  –  Adam  Warski   –  h6p://www.warski.org/blog/2011/04/di-­‐in-­‐scala-­‐cake-­‐pa6ern-­‐pros-­‐cons/  
19. BEKK CONSULTING AS SKUR 39, VIPPETANGEN. P.O. BOX 134 SENTRUM, 0102 OSLO, NORWAY. WWW.BEKK.NO Jan  Fredrik  Wedén   Manager,  Trondheim   @jfweden