What does a double * (splat) operator do

ruby splat
Roy Lee picture Roy Lee · Aug 17, 2013 · Viewed 56.9k times · Source

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?

Answer

Dogbert picture Dogbert · Aug 17, 2013

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}]

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