Make PP more extensible

lib/pp.rb

@@ -93,7 +93,7 @@ def PP.width_for(out)
   #
   # PP.pp returns +out+.
   def PP.pp(obj, out=$>, width=width_for(out))
-    q = PP.new(out, width)
+    q = new(out, width)
     q.guard_inspect_key {q.pp obj}
     q.flush
     #$pp = q
@@ -286,16 +286,21 @@ def pp_hash(obj)
       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

@@ -245,4 +245,29 @@ def test_lasgn_literal
   end
 end
 
+class PPInheritedTest < Test::Unit::TestCase
+  class PPSymbolHash < PP
+    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
+
+  def test_hash_override
+    obj = {k: 1, "": :null, "0": :zero, 100 => :ten}
+    assert_equal <<~EXPECT, PPSymbolHash.pp(obj, "".dup)
+    {k: 1, "": :null, "0": :zero, 100=>:ten}
+    EXPECT
+  end
+end
+
 end