Helper
What
ActionController::Helpers
Basically helpers in Rails are used to extract complex logic out of the view so that you can organize your code better.
Advantages
Extract some complexity out of the view
Make view logic easier to test
Move complexity out of the view
把一些复杂的逻辑从view层中抽出来，放在controller里面：
<% if @user && @user.email.present? %>
<%= @user.email %>
<% end %>
完全可以在controller里面这样：
#site_helper.rb
module SiteHelper
def user_email(user)
user.email if user && user.email.present?
end
end
#user_controller.rb
class UserController
helper SiteHelper
end
有一个method很近似，那就是helper_method
下面来看他们两的区别
helper vs helper_method
helper_method可以把controller中的method share给view
helper则是把整个Hepler 引入到view中，相当于：
``
include_all_helpers
``
