heading.rb in alf-0.11.0

- old
+ new
@@ -1,30 +1,20 @@
 module Alf
-  module Operator::Relational
-    class Heading < Alf::Operator()
-      include Operator::Relational, 
-              Operator::Experimental,
-              Operator::Unary
-    
-      signature do |s|
-      end
+  module Operator
+    module Relational
+      class Heading
+        include Relational, Unary, Experimental
+
+        signature do |s|
+        end
       
-      protected 
-    
-      # See Operator#_prepare
-      def _prepare
-        @tuple_heading = nil
-        each_input_tuple do |tuple|
-          h = tuple_heading(tuple)
-          @tuple_heading ||= h
-          @tuple_heading += h
+        # (see Operator#each)
+        def each
+          yield(operand.inject(Alf::Heading::EMPTY){|h,t|
+            h + Tools.tuple_heading(t)
+          }.to_h)
         end
-      end
 
-      # See Operator#_each
-      def _each
-        yield(@tuple_heading.attributes)
-      end
-
-    end # class Project
-  end # module Operator::Relational
+      end # class Project
+    end # module Relational
+  end # module Operator
 end # module Alf