Inject local variables into rails partial

Question

I want my partial below to get the classy class from it being injected through locals, but I keep getting undefined method for classy.

//view

<%= render layout: "layouts/partial", locals: {className: "classy"} do %>
...
<% end>

//partial

<div class="regular-div <%=className if className?%>"></div>

Answer 1

To check if a local variable is set use local_assigns.has_key?(:some_key) or local_assigns[:some_key] to safely access the local variable.

A nifty way of handling the common task of building a list of classes is:

module ApplicationHelper
  # Takes an array or list of classes and returns a string
  # Example:
  #  class_list('a', 'b', nil, 'c')
  #  => "a b"
  #  class_list(['a', 'b', nil, 'c'])
  #  => "a b c"
  def class_list(*classes)
    [*classes].flatten.compact.join(' ') 
  end
end

Then you can do:

<div class="<%= class_list('regular-div', local_assigns[:className]) %>"></div>