Use symbols for filter names now that ruby has symbol GC

lib/liquid/strainer_template.rb

@@ -24,17 +24,17 @@ module Liquid
 
         include(filter)
 
-        filter_methods.merge(filter.public_instance_methods.map(&:to_s))
+        filter.public_instance_methods.each { |name| filter_methods[name] = true }
       end
 
       def invokable?(method)
-        filter_methods.include?(method.to_s)
+        filter_methods.key?(method.to_sym)
       end
 
       private
 
       def filter_methods
-        @filter_methods ||= Set.new
+        @filter_methods ||= {}
       end
     end
 

lib/liquid/variable.rb

@@ -123,7 +123,7 @@ module Liquid
           filter_args << Expression.parse(a)
         end
       end
-      result = [filter_name, filter_args]
+      result = [filter_name.to_sym, filter_args]
       result << keyword_args if keyword_args
       result
     end