Ruby parameter passing by value or reference? (its by REF)

gistfile1.rb

class Car
  def start(options)
    options[:speed] = 60
    puts "running @ #{options[:speed]}"
  end
end

op = { speed: 50 }
puts op.inspect
Car.new.start op
puts op.inspect


# prints out the following
# {:speed=>50}
# running @ 60
# {:speed=>60}