wrapper.rb

[1] (pry) main: 0> class Hello
[1] (pry) main: 0*   def self.wrapper(method_name)
[1] (pry) main: 0*     old = instance_method(method_name)
[1] (pry) main: 0*     define_method(method_name) do |*args, &block|
[1] (pry) main: 0*       puts "wrapping method lol"
[1] (pry) main: 0*       old.bind(self).call(*args, *block)
[1] (pry) main: 0*     end  
[1] (pry) main: 0*   end  
[1] (pry) main: 0* end  
=> nil
[2] (pry) main: 0> class Goodbye < Hello
[2] (pry) main: 0*   def multiply(x, y)
[2] (pry) main: 0*     2 * x * y
[2] (pry) main: 0*   end  
[2] (pry) main: 0*   def add(x, y)
[2] (pry) main: 0*     2 + x + y
[2] (pry) main: 0*   end  
[2] (pry) main: 0* end  
=> nil
[3] (pry) main: 0> Goodbye.new.multiply(2, 3)
=> 12
[4] (pry) main: 0> Goodbye.new.add(2, 3)
=> 7
[5] (pry) main: 0> class Goodbye
[5] (pry) main: 0*   wrapper(:multiply)
[5] (pry) main: 0*   wrapper(:add)
[5] (pry) main: 0* end 
=> #<Proc:0x000001020f27d0@(pry):4 (lambda)>
[6] (pry) main: 0> Goodbye.new.multiply(2, 3)
wrapping method lol
=> 12
[7] (pry) main: 0> Goodbye.new.add(2, 3)
wrapping method lol
=> 7
[8] (pry) main: 0>