Question

In the following code from ruby docs, why doesn’t orig_exit end up calling itself in infinite recursion?

module Mod
  alias_method :orig_exit, :exit
  def exit(code=0)
    puts "Exiting with code #{code}"
    orig_exit(code)
  end
end
include Mod
exit(99)

Answer 1

why doesn’t orig_exit end up calling itself in infinite recursion?

Because there is no recursion here.

First, exit is called, from the last line (exit(99)) which in turn calls orig_exit, which is a different function. Unless orig_exit explicitly calls exit (which there is no reason to believe it does) there is no possibility for recursion. When orig_exit returns, its return value is returned from exit as well.

alias_method has renamed the method that was named exit to orig_exit, and then a completely new function named exit is defined.