Equals, Tuples and Case-classes

This is mostly a quick tip (or opportunity for refactoring).

Most of Scala's built in classes implement a useful equals and hashcode. The very commonly used case-classes and Tuple classes are the examples that spring to mind. So this enables the following options:

1. // Assume Box is out of your control and you cannot refactor it into a case class
2. scala> class Box(val name:String, val minx:Int, val miny:Int, val maxx:Int, val maxy:Int)
3. defined class Box
5. scala> val box = new Box("mybox", 0, 0, 10, 10)
6. box: Box = Box@568bf3ec
8. // before:
9. scala> box.minx == 0 && box.miny == 0 && box.maxx == 10 && box.maxy == 10      
10. res3: Boolean = true
12. // after
13. scala> import box._
14. import box._
16. scala> (minx,miny,maxx,maxy) == (0,0,10,10)
17. res5: Boolean = true
19. // another box definition:
20. scala> case class Box2 (name:String, ul:(Int,Int), lr:(Int,Int)) 
21. defined class Box2
23. // case classes have nice equals for comparison
24. scala> box2 == Box2("a nicer box", (0,0), (10,10))
25. res6: Boolean = true
27. // but what if you don't want to compare names
28. scala> import box2._
29. import box2._
31. scala> (ul,lr) == ((0,0),(10,10))
32. res7: Boolean = true

Equals

One welcome change in Scala is the change of semantics of the == operator. In Scala it is the same as doing a .equals comparison in Java. If you want identity comparison you can use the eq method (and ne for the not equal comparator).

Examples:

1. scala> case class Name(first:String, last:String)
2. defined class Name
4. scala> val jesse = Name("Jesse","Eichar")
5. jesse: Name = Name(Jesse,Eichar)
7. scala> val jesse2 = Name("Jesse","Eichar")
8. jesse2: Name = Name(Jesse,Eichar)
10. scala> val jody = Name("Jody","Garnett")
11. jody: Name = Name(Jody,Garnett)
13. scala> val jJames = Name("Jesse","James")
14. jJames: Name = Name(Jesse,James)
16. scala> jesse == jesse2
17. res0: Boolean = true
19. scala> jesse == jody
20. res1: Boolean = false
22. scala> jesse ne jesse2
23. res2: Boolean = true
25. scala> jesse eq jesse2
26. res3: Boolean = false