When do I have to treat my methods as partially applied functions in Scala?

Question

I noticed that when I\'m working with functions that expect other functions as parameters, I can sometimes do this:

someFunction(firstParam,anotherFunction)
         


        

Answer 1

The rule is actually simple: you have to write the _ whenever the compiler is not explicitly expecting a Function object.

Example in the REPL:

scala> def f(i: Int) = i    
f: (i: Int)Int

scala> val g = f
:6: error: missing arguments for method f in object $iw;
follow this method with `_' if you want to treat it as a partially applied function
       val g = f
               ^

scala> val g: Int => Int = f  
g: (Int) => Int =