An alternative to the builder pattern, e.g. for configuration APIs.

gistfile1.rb

class Capybara
  class << self
    attr_accessor :default_wait_time

    def magic(a,&b)
      puts "doing magic for #{a}"
      yield
      puts "mischief managed"
    end

    def configure &b
      instance_exec &b
    end
  end
end

Capybara.configure do
  @default_wait_time = 23
  magic "foo" do
    puts "abra cadabra!"
  end
end

p Capybara.default_wait_time