refactoring expressions to a module

lib/arel.rb

 require 'arel/crud'
 
 require 'arel/version'
+require 'arel/expressions'
 require 'arel/table'
 require 'arel/attributes'
 require 'arel/compatibility/wheres'

lib/arel/attributes/attribute.rb

 module Arel
   module Attributes
     class Attribute < Struct.new :relation, :name, :column
+      include Arel::Expressions
+
       def not_eq other
         Nodes::NotEqual.new self, other
       end
@@ -13,26 +15,6 @@ def in other
         Nodes::In.new self, other
       end
 
-      def count distinct = false
-        Nodes::Count.new [self], distinct
-      end
-
-      def sum
-        Nodes::Sum.new [self], Nodes::SqlLiteral.new('sum_id')
-      end
-
-      def maximum
-        Nodes::Max.new [self], Nodes::SqlLiteral.new('max_id')
-      end
-
-      def minimum
-        Nodes::Min.new [self], Nodes::SqlLiteral.new('min_id')
-      end
-
-      def average
-        Nodes::Avg.new [self], Nodes::SqlLiteral.new('avg_id')
-      end
-
       def gteq right
         Nodes::GreaterThanOrEqual.new self, right
       end

lib/arel/expressions.rb

+module Arel
+  module Expressions
+    def count distinct = false
+      Nodes::Count.new [self], distinct
+    end
+
+    def sum
+      Nodes::Sum.new [self], Nodes::SqlLiteral.new('sum_id')
+    end
+
+    def maximum
+      Nodes::Max.new [self], Nodes::SqlLiteral.new('max_id')
+    end
+
+    def minimum
+      Nodes::Min.new [self], Nodes::SqlLiteral.new('min_id')
+    end
+
+    def average
+      Nodes::Avg.new [self], Nodes::SqlLiteral.new('avg_id')
+    end
+  end
+end

lib/arel/nodes/sql_literal.rb

 module Arel
   module Nodes
     class SqlLiteral < String
-      def count distinct = false
-        Count.new [self], distinct
-      end
-
-      def sum
-        Nodes::Sum.new [self], Nodes::SqlLiteral.new('sum_id')
-      end
-
-      def maximum
-        Nodes::Max.new [self], Nodes::SqlLiteral.new('max_id')
-      end
+      include Arel::Expressions
     end
   end
 end