[ruby/pp] Extract pp_hash_pair

The method which prints single pair of a hash, to make extending
pretty printing Hash easier, apart from Hash construct itself.

https://github.com/ruby/pp/commit/3fcf2d1142

lib/pp.rb

@@ -286,16 +286,21 @@ class PP < PrettyPrint
       group(1, '{', '}') {
         seplist(obj, nil, :each_pair) {|k, v|
           group {
-            pp k
-            text '=>'
-            group(1) {
-              breakable ''
-              pp v
-            }
+            pp_hash_pair k, v
           }
         }
       }
     end
+
+    # A pretty print for a pair of Hash
+    def pp_hash_pair(k, v)
+      pp k
+      text '=>'
+      group(1) {
+        breakable ''
+        pp v
+      }
+    end
   end
 
   include PPMethods

test/test_pp.rb

@@ -247,25 +247,18 @@ end
 
 class PPInheritedTest < Test::Unit::TestCase
   class PPSymbolHash < PP
-    def pp_hash(obj)
-      group(1, "{", "}") {
-        seplist(obj, nil, :each_pair) {|k, v|
-          case k
-          when Symbol
-            text k.inspect.delete_prefix(":")
-            text ":"
-            sep = " "
-          else
-            pp k
-            text "=>"
-            sep = ""
-          end
-          group(1) {
-            breakable sep
-            pp v
-          }
+    def pp_hash_pair(k, v)
+      case k
+      when Symbol
+        text k.inspect.delete_prefix(":")
+        text ":"
+        group(1) {
+          breakable
+          pp v
         }
-      }
+      else
+        super
+      end
     end
   end