rails flash messages with bootstrap 4

_flash.html.erb

<div class="container">
  <% flash.each do |type, msg| %>
    <div class="alert <%= bootstrap_class_for_flash(type) %> alert-dismissable fade show">
      <%= msg %>
      <button class="close" data-dismiss="alert">x</button>
    </div>
  <% end %> 
</div>

application.html.erb

<%= render partial: 'flash', flash: flash %> 

application_helper.rb

module ApplicationHelper
  def bootstrap_class_for_flash(flash_type)
    case flash_type
    when 'success'
      'alert-success'
    when 'error'
      'alert-danger'
    when 'alert'
      'alert-warning'
    when 'notice'
      'alert-info'
    else
      flash_type.to_s
    end
  end
end