class ActionController::Renderer


ApplicationController.renderer.new(method: ‘post’, https: true)
* by initializing an instance of renderer by passing it a custom environment.
ApplicationController.renderer.defaults # => hash with default Rack environment
* by changing renderer defaults, like
ActionController::Renderer#env. You can set it up in two ways:
The template will be rendered in a Rack environment which is accessible through
FooController.render :action, locals: { … }, assigns: { … }
For example:
#render allows you to use the same options that you can use when rendering in a controller.
ApplicationController.render template: ‘…’
You can use this shortcut in a controller, instead of the previous example:
ApplicationController.renderer.render template: ‘…’
It allows you to call method #render directly.
ApplicationController.renderer
For example:
You get a concrete renderer class by invoking ActionController::Base#renderer.
without requirement of being in controller actions.
ActionController::Renderer allows you to render arbitrary templates

def self.for(controller, env = {}, defaults = DEFAULTS.dup)

Create a new renderer instance for a specific controller class. 
def self.for(controller, env = {}, defaults = DEFAULTS.dup)
  new(controller, env, defaults)
end

def initialize(controller, env, defaults)

+ActionController::Renderer::DEFAULTS+.
It will be merged with the default Rack environment defined by
Accepts a custom Rack environment to render templates in. 
def initialize(controller, env, defaults)
  @controller = controller
  @defaults = defaults
  @env = normalize_keys defaults, env
end

def new(env = {})

Create a new renderer for the same controller but with a new env. 
def new(env = {})
  self.class.new controller, env, defaults
end

def normalize_keys(defaults, env) 

def normalize_keys(defaults, env)
  new_env = {}
  env.each_pair { |k, v| new_env[rack_key_for(k)] = rack_value_for(k, v) }
  defaults.each_pair do |k, v|
    key = rack_key_for(k)
    new_env[key] = rack_value_for(k, v) unless new_env.key?(key)
  end
  new_env["rack.url_scheme"] = new_env["HTTPS"] == "on" ? "https" : "http"
  new_env
end

def rack_key_for(key) 

def rack_key_for(key)
  RACK_KEY_TRANSLATION[key] || key.to_s
end

def rack_value_for(key, value) 

def rack_value_for(key, value)
  case key
  when :https
    value ? "on" : "off"
  when :method
    -value.upcase
  else
    value
  end
end

def render(*args)

Renders a template to a string, just like ActionController::Rendering#render_to_string. 
def render(*args)
  raise "missing controller" unless controller
  request = ActionDispatch::Request.new @env
  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)

Create a new renderer for the same controller but with new defaults. 
def with_defaults(defaults)
  self.class.new controller, @env, self.defaults.merge(defaults)
end