Earlier quoted context omitted.
> The first two uses of () are anonymous functions No they're not. They are just containers for arguments to a function. In Scala whenever you call a function which takes as it's only parameter another function, you can even replace them entirely with curly brackets: scala> (1 to 5).map(_ * 5) res1: scala.collection.immutable.IndexedSeq[Int] = Vector(5, 10, 15, 20, 25) is equivalent to: scala> 1 to 5 map { _ * 5 } re…
"Perhaps your original point stands that in Clojure you have _better_ visual clues for picking out anonymous functions at a glance" Yes, this is what I was trying to get at. Thanks for clarifying the examples, though. So, using _ in any expression makes that expression an anonymous function? Is _ by itself the identity 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)
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
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
scala> (1 to 5).foldLeft(0)(_ + _)
res19: Int = 15