undef_method

gistfile1.txt

jruby-1.7.0.preview1 :001 > class A 
jruby-1.7.0.preview1 :002?>   end
 => nil 
jruby-1.7.0.preview1 :003 > class Object
jruby-1.7.0.preview1 :004?>   def to_json
jruby-1.7.0.preview1 :005?>     raise "don't call me"
jruby-1.7.0.preview1 :006?>     end
jruby-1.7.0.preview1 :007?>   end
 => nil 
jruby-1.7.0.preview1 :008 > a=A.new
 => #<A:0x1d9dbdc4> 
jruby-1.7.0.preview1 :009 > a.to_json
RuntimeError: don't call me
[...]
jruby-1.7.0.preview1 :011 >   class << a
jruby-1.7.0.preview1 :012?>   undef_method :to_json
jruby-1.7.0.preview1 :013?>   end
 => #<Class:#<A:0x1d9dbdc4>> 
jruby-1.7.0.preview1 :014 > a.to_json
NoMethodError: undefined method `to_json' for #<A:0x1d9dbdc4>
[...]
 => false