Undef singleton method from ruby ​​object

Question

I would like to be able to undef the oneton method for this object.

class A end a = A.new def a.foo puts "bar" end # undef a.foo here a.foo # should crash 

Answer 1

 class A end a = A.new def a.foo puts "bar" end a.instance_eval { undef :foo } a.foo # => undefined method `foo' for #<A:0x8469c60> (NoMethodError) 

Answer 2

 class << a undef foo end 

As an alternative:

 a.singleton_class.send :undef_method, :foo