Functions using case statements

A further tip regarding using case statements to construct functions. If a case statement is assigned to a Function it will construct a Function object not a PartialFunction.

I suppose the question is why do you care about this since PartialFunction is a Function. The fact is that a PartialFunction is a Function1. But using a case statement you can construct a Function4 very easily.

1. scala> def run(f : Function1[Any,Unit]) = println(f.isInstanceOf[PartialFunction[_,_]])
2. run: (f: (Any) => Unit)Unit
4. /*
5. since run expects a Function calling run as shown here will make a 
6. Function object not a PartialFunction Object
7. */
8. scala> run({case f => ()}) 
9. false
11. scala> def pf(f : PartialFunction[Any,Unit]) = println(f.isInstanceOf[PartialFunction[_,_]]) 
12. pf: (f: PartialFunction[Any,Unit])Unit
14. // Now a PartialFunction will be created
15. scala> pf({case f => ()})                                                                         
16. true
18. scala> def run(f : Function2[Int,String,Unit]) = f(1,"2")                                     
19. run: (f: (Int, String) => Unit)Unit
21. /*
22. This demonstrates why it is important that a case creates a Function
23. when assigned to a Function. PartialFunctions are Function1 objects
24. but the following statement is creating a Function2 object.
25. */
26. scala> run({                 
27.      | case (1,b) => println(b)
28.      | case (a,b) => println(a,b)
29.      | })
30. 2