Wtf Ruby

test.rb

def f(a = "", b = {}, c = "", d = "")
  puts "a=#{a}"
  puts "b=#{b}"
  puts "c=#{c}"
  puts "d=#{d}"
end

f(c: "c", d: "d")

test.rb-output

a={:c=>"c", :d=>"d"}
b={}
c=
d=
=> nil