Use a type widening lookup strategy to DRY up printers

lib/mutant/reporter/cli/printer.rb

@@ -63,10 +63,34 @@ module Mutant
         # @api private
         #
         def self.visit(object, output)
-          printer = REGISTRY.fetch(object.class)
+          printer = lookup(object.class)
           printer.run(object, output)
         end
 
+        # Lookup printer class
+        #
+        # @param [Class] klass
+        #
+        # @return [Class:Printer]
+        #   if found
+        #
+        # @raise [RuntimeError]
+        #   otherwise
+        #
+        # @api private
+        #
+        def self.lookup(klass)
+          current = klass
+          until current == Object
+            if REGISTRY.key?(current)
+              return REGISTRY.fetch(current)
+            end
+            current = current.superclass
+          end
+          raise "No printer for: #{klass}"
+        end
+        private_class_method :lookup
+
         abstract_method :run
 
       private

lib/mutant/reporter/cli/printer/killer.rb

@@ -8,7 +8,7 @@ module Mutant
         # Printer for killer results
         class Killer < self
 
-          handle(Mutant::Killer::Forked)
+          handle(Mutant::Killer)
 
           SUCCESS = '.'.freeze
           FAILURE = 'F'.freeze

lib/mutant/reporter/cli/printer/mutation.rb

@@ -20,14 +20,7 @@ module Mutant
           #
           def self.build(runner, output)
             mutation = runner.mutation
-            case mutation
-            when Mutant::Mutation::Neutral::Noop
-              Noop
-            when Mutant::Mutation::Evil, Mutant::Mutation::Neutral
-              Diff
-            else
-              raise "Unknown mutation: #{mutation}"
-            end.new(runner, output)
+            lookup(mutation.class).new(runner, output)
           end
 
           # Run mutation printer
@@ -56,12 +49,14 @@ module Mutant
           # Reporter for noop mutations
           class Noop < self
 
-          MESSAGE = [
-            'Parsed subject AST:',
-            '%s',
-            'Unparsed source:',
-            '%s',
-          ].join("\n")
+            handle(Mutant::Mutation::Neutral::Noop)
+
+            MESSAGE = [
+              'Parsed subject AST:',
+              '%s',
+              'Unparsed source:',
+              '%s',
+            ].join("\n")
 
           private
 
@@ -84,6 +79,9 @@ module Mutant
           # Reporter for neutral and evil mutations
           class Diff < self
 
+            handle(Mutant::Mutation::Neutral)
+            handle(Mutant::Mutation::Evil)
+
             # Return diff
             #
             # @return [String]

lib/mutant/reporter/cli/printer/subject.rb

@@ -8,9 +8,7 @@ module Mutant
         # Subject results printer
         class Subject < self
 
-          handle(Mutant::Subject::Method::Instance)
-          handle(Mutant::Subject::Method::Instance::Memoized)
-          handle(Mutant::Subject::Method::Singleton)
+          handle(Mutant::Subject)
 
           # Run subject results printer
           #