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functions, methods

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Functions

def double(n: Int): Int = {
  2 * n
}

val x = 4
println(double(x))    // 8

If the function's body is just one expression, then you can omit the curly braces:

def double(n: Int): Int = 2 * n    // equivalent with the previous

Methods

def hello(name: String) {
  println("Hello, %s!".format(name))
}

Notice that its return type is missing and there is no "=" sign before the opening brace. This is a method, not a function.

The code above is actually a shorthand for the following. Here it is explicitly stated that its return type is Unit (i.e. void):

def hello(name: String): Unit = {
  println("Hello, %s!".format(name))
}