> So, using _ in any expression makes that expression an anonymous function? Ah, I should have said - the syntax above only works with one-liners. The followin

> So, using _ in any expression makes that expression an anonymous function? Ah, I should have said - the syntax above only works with one-liners. The following wouldn't work: scala> apply(val y = _ * 50; y * 100, 10) scala> apply((val y = _ * 50; y * 100), 10) scala> apply((x: Int) => val y = x * 50; y * 100, 10) etc. Instead you would need to explicitly surround the method body with curly brackets: scala> apply((x:Int) => { val y = x * 20; y }, 10) res18: Int = 200 And in this case, it's obvious what is happening. So it's more like providing a one line expression where a function is expected makes it an anonymous function. The use of _ is simply a shortcut when you don't need to assign parameters to a local variable. It even works with multiple parameters. I.e. compare: scala> (1 to 5).foldLeft(0)((accumulator:Int,x:Int) => accumulator + x) res22: Int = 15 To: scala> (1 to 5).foldLeft(0)(_ + _) res19: Int = 15