Endpoint DSL example

dsl.rb

module DSL
  # We put our DSL syntax (methods) in a separate module (ClassMethods) because it 
  #   will be converted to class methods once a class includes it.
  module ClassMethods
    attr_reader :routes

    ##### SUPPORTED DSL SYNTAX
    def get(uri, &block)
      save_route(:get, uri, block)
    end

    def post(uri, &block)
      save_route(:post, uri, block)
    end
    ##### END DSL METHODS

    # A private helper method that is only available to these two methods
    private

    def save_route(http_method, uri, block)
      @routes[http_method][uri] = block
    end
  end
end  

module DSL
  module ClassMethods
    ...
  end

  # This method will be automatically executed anytime a class includes the DSL module
  def self.included(base)
    # Our DSL methods which are in the ClassMethods module will be 
    #  extended as class methods to the base class once mixed in
    base.send :extend, ClassMethods

    # Declare a class variable in the base class for us to store our routes. If this was a class
    #   variable in the DSL module every class mixing it in would end up sharing the same routes
    base.class_eval do
      @routes = { get: {}, post: {} }
    end
  end  
end

module DSL 
  module ClassMethods
    ...
  end

  def self.included(base)
    ...
  end

  # List all the routes
  def routes
    self.class.routes
  end

  def execute_route(http_method, uri, params = nil)
    block = self.class.routes[http_method][uri]

    # Execute our method in the context of the instance class so we have access
    #   to variables and local methods
    instance_exec(params, &block)
  end  
end

class UsersEndpoint
  include DSL

  def initialize
    # An array to store users in
    @users = []
  end

  # Endpoint to list all users
  get '/users' do
    @users
  end

  # Endpoint to create a new user
  post '/users' do |id: nil, name: nil|
    create_user(id, name)
  end

  private

  def create_user(id, name)
    @users << { id: id, name: name }
  end
end