Refine Set#pretty_print check

Author: nobu

lib/pp.rb

@@ -443,6 +443,13 @@ def pretty_print_cycle(q) # :nodoc:
  end
 end
 
+if defined?(Set)
+ if set_pp = Set.instance_method(:initialize).source_location
+ set_pp = !set_pp.first.end_with?("/set.rb") # not defined in set.rb
+ else
+ set_pp = true # defined in C
+ end
+end
 class Set # :nodoc:
  def pretty_print(pp) # :nodoc:
  pp.group(1, '#<Set:', '>') {
@@ -453,12 +460,12 @@ def pretty_print(pp) # :nodoc:
  }
  }
  }
- end unless method_defined?(:pretty_print)
+ end
 
  def pretty_print_cycle(pp) # :nodoc:
  pp.text sprintf('#<Set: {%s}>', empty? ? '' : '...')
- end unless method_defined?(:pretty_print_cycle)
-end
+ end
+end if set_pp
 
 class << ENV # :nodoc:
  def pretty_print(q) # :nodoc: