[Function Values]Using Functions as Variables

you can think of the => symbol as a transformer. In this case, the function transforms the Int value i to an Int value that is twice the value of i.

(i: Int) => { i * 2 }

You can now assign that function literal to a variable:

val double = (i: Int) => { i * 2 }

The variable double is an instance, just like an instance of a String, Int, or other type, but in this case, it’s an instance of a function, known as a function value. You can now invoke double just like you’d call a method:

double(2) // 4

double(3) // 6

Beyond just invoking double like this, you can also pass it to any method (or function) that takes a function parameter with its signature.

scala> val list = List.range(1, 5)

list: List[Int] = List(1, 2, 3, 4)

scala> list.map(double)

res0: List[Int] = List(2, 4, 6, 8)