New way for arguments forwarding in Ruby 2.7

Ruby 2.7 introduced a shorthand syntax (...) for forwarding parameters to methods.

def hello(...)
  p(...)
end

hello "world"
hello %i[foo bar]

=> "world"
=> [:foo, :bar]

... vs args and kwargs

It might look similar to existing args and kwargs so let’s compare them on an example:

def greet(*args, **kwargs, &block)
  print "Args:"
  p args

  print "Kwargs:"
  p kwargs

  print "Block:"
  p block
end

hello "world"
hello "world", at: 8
hello "world", at: 8 do
  "Good morning!"
end

greet "world"
greet "world", at: 8
greet "world", at: 8 do
  "Good morning!"
end

=>
"world"
=>
"world"
{:at=>8}
=>
"world"
{:at=>8}
=>
Args:["world"]
Kwargs:{}
Block:nil
=>
Args:["world"]
Kwargs:{:at=>8}
Block:nil
=>
Args:["world"]
Kwargs:{:at=>8}
Block:#<Proc:0x00007fdcadc1d0e0 (irb):56>

As shown above, ... syntax is limited to simple forwarding arguments to a method at least until leading arguments support from Ruby 3 gets backported.