rubysplat

What does a double * (splat) operator do

Have you seen a function declared like this?

def foo a, **b
  ...
end

I understand that a single * is the splat operator. What does ** mean?

Solution

  • Ruby 2.0 introduced keyword arguments, and ** acts like *, but for keyword arguments. It returns a Hash with key / value pairs.

    For this code:

    def foo(a, *b, **c)
  [a, b, c]
end

    Here's a demo:

    > foo 10
=> [10, [], {}]
> foo 10, 20, 30
=> [10, [20, 30], {}]
> foo 10, 20, 30, d: 40, e: 50
=> [10, [20, 30], {:d=>40, :e=>50}]
> foo 10, d: 40, e: 50
=> [10, [], {:d=>40, :e=>50}]