class ActionController::Renderer


PostsController.render :show, assigns: { post: Post.first }
ApplicationController.render template: “posts/show”, assigns: { post: Post.first }
As a shortcut, you can also call render directly on the controller class itself:
PostsController.renderer.render :show, assigns: { post: Post.first }
ApplicationController.renderer.render template: “posts/show”, assigns: { post: Post.first }
and render a template by calling the #render method:
PostsController.renderer
ApplicationController.renderer
You can get a renderer instance by calling renderer on a controller class:
being inside a controller action.
ActionController::Renderer allows you to render arbitrary templates without
= Action Controller Renderer

def self.for(controller, env = nil, defaults = DEFAULTS)

Creates a new renderer using the given controller class. See ::new. 
def self.for(controller, env = nil, defaults = DEFAULTS)
  new(controller, env, defaults)
end

def self.normalize_env(env) # :nodoc:

:nodoc: 
def self.normalize_env(env) # :nodoc:
  new_env = {}
  env.each_pair do |key, value|
    case key
    when :https
      value = value ? "on" : "off"
    when :method
      value = -value.upcase
    end
    key = RACK_KEY_TRANSLATION[key] || key.to_s
    new_env[key] = value
  end
  if new_env["HTTP_HOST"]
    new_env["HTTPS"] ||= "off"
    new_env["SCRIPT_NAME"] ||= ""
  end
  if new_env["HTTPS"]
    new_env["rack.url_scheme"] = new_env["HTTPS"] == "on" ? "https" : "http"
  end
  new_env
end

def defaults 

def defaults
  @defaults = @defaults.dup if @defaults.frozen?
  @defaults
end

def env_for_request 

def env_for_request
  if @env.key?("HTTP_HOST") || controller._routes.nil?
    @env.dup
  else
    controller._routes.default_env.merge(@env)
  end
end

def initialize(controller, env, defaults)

specify a +protocol+.
+Rails.application.config.force_ssl+ if +default_url_options+ does not
not specified. Additionally, the +https+ boolean will fall back to
+script_name+ will also be derived from +default_url_options+ if they were
routes' +default_url_options+. In this case, the +https+ boolean and the
If no +http_host+ is specified, the env HTTP host will be derived from the

+defaults+ will be retained when calling #new on a renderer instance.
the same format as +env+. +env+ will be merged on top of these values.
* +defaults+ - Default values for the Rack env. Entries are specified in
* +:input+ - The input stream. Converts to Rack's +rack.input+.
corresponds to the application. Converts to Rack's +SCRIPT_NAME+.
* +:script_name+ - The portion of the incoming request's URL path that
Converts to Rack's +REQUEST_METHOD+.
* +:method+ - The HTTP method for the incoming request, case-insensitive.
Converts to Rack's +HTTPS+.
* +:https+ - Boolean indicating whether the incoming request uses HTTPS.
Rack's +HTTP_HOST+.
* +:http_host+ - The HTTP host for the incoming request. Converts to
the following, which will be converted appropriately:
Entries can be typical Rack env keys and values, or they can be any of
* +env+ - The Rack env to use for mocking a request when rendering.
* +controller+ - The controller class to instantiate for rendering.

==== Parameters

Initializes a new Renderer. 
def initialize(controller, env, defaults)
  @controller = controller
  @defaults = defaults
  if env.blank? && @defaults == DEFAULTS
    @env = DEFAULT_ENV
  else
    @env = normalize_env(@defaults)
    @env.merge!(normalize_env(env)) unless env.blank?
  end
end

def new(env = nil)


ApplicationController.renderer.new(method: "post")

Creates a new renderer using the same controller, but with a new Rack env. 
def new(env = nil)
  self.class.new controller, env, @defaults
end

def render(*args)

Renders a template to a string, just like ActionController::Rendering#render_to_string. 
def render(*args)
  request = ActionDispatch::Request.new(env_for_request)
  request.routes = controller._routes
  instance = controller.new
  instance.set_request! request
  instance.set_response! controller.make_response!(request)
  instance.render_to_string(*args)
end

def with_defaults(defaults)

defaults merged on top of the previous defaults.
Creates a new renderer using the same controller, but with the given 
def with_defaults(defaults)
  self.class.new controller, @env, @defaults.merge(defaults)
end