Using hash keys to create instance variables

request_double.rb

# Test double for a request
class RequestDouble
  attr_accessor :env

  def initialize hash
    @env = {}

    # Turn each hash entry into an instance variable
    hash.each do |key, value|
      instance_variable_set "@#{key}", value
      self.class.class_eval do
        attr_accessor key
      end
    end
  end
end