p.163 Change the parameter of "count_descendants_matching" to block.

chapter6/Extract_Surrounding_Method.rb

@@ -20,18 +20,18 @@ def number_of_living_descendants
   end
 
   def number_of_descendants_named(name)
-    count_descendants_matching(name)
+    count_descendants_matching{|descendant| descendant.name == name}
   end
 
   def alive?
     @date_of_death.nil?
   end
 
   protected
-  def count_descendants_matching(name)
+  def count_descendants_matching(&block)
     children.inject(0) do |count, child|
-      count += 1 if child.name == name
-      count += child.count_descendants_matching(name)
+      count += 1 if yield child
+      count += child.count_descendants_matching(&block)
     end
   end
 end