env.rb

module Env
  class EnvKeyError < StandardError; end
  def self.method_missing(method_name, *arguments, &block)
    env_value(method_name) { raise EnvKeyError, method_name }
  end

  def self.respond_to?(method_name, include_private = false)
    env_value(method_name)
    true
  rescue StandardError
    false
  end

  def self.method_to_key(method_name)
    method_name.to_s.upcase
  end

  def self.env_value(method_name, &block)
    block ||= -> { false }
    ENV.fetch(method_to_key(method_name), &block)
  end
end