Metaprogramming is code using define_method (optionally closing over local variables), instance_eval, and stuff of that nature. Even with bytecode manipulation

Metaprogramming is code using define_method (optionally closing over local variables), instance_eval, and stuff of that nature. Even with bytecode manipulation they would be very difficult to emulate in Java/C++ and would be quite slow. That said, JavaScript is not far off of Ruby's monkeying capabilities and yet pretty darned fast.