Ruby's discreet argument forwarding shorthand...

Alexandre Ignjatovic — Fri, 08 Mar 2024 09:14:22 +0000

Yes, those three dots are intentional. Yes it's a pun. No I won't stop. Yes, you'll understand if you read this article to the end.

The problem

Have you ever ended up writing tons of methods doing mostly parameter forwarding?

class Foo
  attr_reader :bar

  # That's the one:
  def do_stuff(x, y:)
    bar.do_stuff(x, y:)
  end
end

Ruby's Forwardable module may be the solution to writing simpler code:

require 'forwardable'

class Foo
  attr_reader :bar
  extend Forwardable
  def_delegator :@bar, :do_stuff
end

But what if I'd like to "do stuff" twice? Or add a log line?

Recently, I learned that Ruby includes an argument forwarding shorthand since its version 2.7! (Which exists since 2019)

This shorthand is .... Simple as that, and you can add your log line without bothering with how the arguments are going to evolve in the future:

def do_stuff(...)
  puts 'My log line'
  bar.do_stuff(...)
end

The good thing is: if bar#do_stuff is added another argument, my foo#do_stuff method do NOT have to change!

But what if I'd like to access one of the arguments before forwarding it?

Since its version 3.0, Ruby gained support for leading arguments:

def do_stuff(x, ...)
  bar.do_stuff(x, ...)
end

Hope you'll use it a lot...