TableBuilderHelper: Move `referential` variable to method

At Robert's recommendation, use `try` instead of `respond_to?` because
it's shorter.

Also at Robert's recommendation, move the `referential` variable to a
method to memoize it. This allows us to use it in other places without
re-getting it and without having to do the `if` check again.

He had suggested:

    def referential
      return @__referential__ if instance_variable_defined?(:@__referential__)
      @__referential__ = try(:current_referential)
    end

but I think the `||=` version works the same way and is shorter. Still
need to find out from him what our style guide rules for __variables__
are and why I should be using one here.

Refs #3479

1 files changed, 6 insertions, 4 deletions

diff --git a/app/helpers/table_builder_helper.rb b/app/helpers/table_builder_helper.rb
index e1b8b406d..d82f1eb03 100644
--- a/app/helpers/table_builder_helper.rb
+++ b/app/helpers/table_builder_helper.rb
@@ -104,10 +104,6 @@ module TableBuilderHelper
   end
 
   def tbody(collection, columns, selectable, links)
-    # Certain controllers don't define a `#current_referential`. In these
-    # cases, avoid a `NoMethodError`.
-    referential = current_referential if respond_to?(:current_referential)
-
     content_tag :tbody do
       collection.map do |item|
 
@@ -238,4 +234,10 @@ module TableBuilderHelper
       class: ('delete-action' if link.method == :delete)
     )
   end
+
+  def referential
+    # Certain controllers don't define a `#current_referential`. In these
+    # cases, avoid a `NoMethodError`.
+    @__referential__ ||= try(:current_referential)
+  end
 end