Create a class with no instance methods in Ruby

Question

How can I create a class with no instance methods defined? Not even __send__ or __id__ .

Answer 1

You can use Module# undef_method to undefine methods:

class Foo < BasicObject
  instance_methods.each { |method| undef_method(method) }
end

Foo.instance_methods #=> []
foo = Foo.new
foo.__id__           #=> NoMethodError: undefined method `__id__' for #<Foo:0x007fb9da565dd8>
foo.__send__(:test)  #=> NoMethodError: undefined method `__send__' for #<Foo:0x007fb9da565dd8>

In this example Foo inherits from BasicObject , because this class itself has very few instance methods defined and thus, undefining them is faster. This is not obligatory, meaning, that you can undefine instance methods from any class no matter what it inherits from, so it could be very well written as:

class Foo
  instance_methods.each { |method| undef_method(method) }
end