Anonymous Block Forwarding in Ruby

You probably have used (or at least heard about) the argument forwarding feature in Ruby, which was added in Ruby 2.7, that lets you forward all the arguments passed to a method, as they are, to another method, using the three dots ... syntax.

This includes all positional, named, and even block arguments.

def execute(action="", **options)
  p action   # get
  p options  # {:url=>"/test", :values=>[201, 202]}
  
  yield "fake response"
end

def perform(...)
  # execute receives all the arguments 
  # received by the perform function
  execute(...)
end

perform action="get", url: "/test", values: [201, 202] do |result|
  p result  # "fake response"
end

Did you know that there's a similar shorthand to forward a block anonymously? I learned this very recently (yesterday!), and I love it.

Notice the perform method in the following example:

def execute(&blk)
  yield "response 1"
  blk.call "response 2"
end

def perform(&)
  # execute receives the same block
  # received by the perform function
  execute(&)
end

perform do |result|
  p result  
end

# Output:
# "response 1"
# "response 2"

Earlier, you'd have done something like:

def perform(&blk)
  execute(&blk)
end

But starting in Ruby 3.1, you can do this:

def perform(&)
  execute(&)
end

Pretty cool, right? Also looks pretty nice, in my opinion. What do you think?

If you like this syntax, and would like to enforce it via Rubocop (Rails 8 ships with a default Rubocop linter out of box), you can use the following Rule:

Naming/BlockForwarding:
  EnforcedStyle: anonymous

On the other hand, if you prefer the older explicit version, enforce it with this rule:

Naming/BlockForwarding:
  EnforcedStyle: explicit

P.S. For an in-depth explanation, I suggest reading this post from zverok. It goes into much more depth.

That's a wrap. I hope you found this article helpful and you learned something new.

As always, if you have any questions or feedback, didn't understand something, or found a mistake, please leave a comment below or send me an email. I reply to all emails I get from developers, and I look forward to hearing from you.

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