gistfile1.rb

#! /usr/bin/env ruby

require "pp"

class Request
  def env
    { "place" => "tarolandia" }
  end

  def params
    { "name" => "taro" }
  end
end

request = Request.new

request.params["name"] = "Lautaro"

pp request.params # => {"name"=>"taro"}

$ps = request.params.dup
$ps["name"] = "inkel"

def request.params
  $ps
end

pp request.params # => {"name"=>"inkel"}

gistfile2.rb

#! /usr/bin/env ruby

require "pp"

class Request
  def env
    { "place" => "tarolandia" }
  end

  def params
    { "name" => "taro" }
  end
end

request = Request.new

request.params["name"] = "Lautaro"

pp request.params # => {"name"=>"taro"}

def filter(request)
  request.params.tap do |hash|
    hash["name"] = "inkel"
  end
end

def request.params
  filter(self.dup)
end

pp request.params # => {"name"=>"inkel"}