Passing local optional variables to sub template views.

compared_to_defined_method_with_oneline_condition.erb

# this will work
<% unless defined?(:show_author) %>
  <% show_author = true %>
<% end %>

# NOT work
<% show_author = true unless defined?(:show_author) %>

# this will work
<% show_author = true unless local_assigns.has_key? :show_author %>

solution.erb

# http://api.rubyonrails.org/classes/ActionView/Base.html

# If you need to find out whether a certain local variable
# has been assigned a value in a particular render call, 
# you need to use the following pattern:

<% unless local_assigns.has_key? :show_author %>
  <% show_author = true %>
<% end %>

<% if show_author %>
  Author: <%= @article.author %>
<% end %>

# Testing using defined? headline will not work. This is an implementation restriction.

use_case_sample.erb

<%= render 'article', :show_author => false %>
<%= render 'article' %>