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rubyeval

How to get `main` object evaluated in Ruby?

How to know or get main, mean top-level binding, object evaluated in Ruby?

Example:

$ irb
irb(main):001:0> self
=> main
irb(main):002:0> eval "self"
=> main
irb(main):003:0> eval "main"
NameError: undefined local variable or method `main' for main:Object
        from (irb):3:in `eval'
        from (irb):3:in `eval'
        from (irb):3
    from /home/malo/.rvm/rubies/ruby-1.9.3-p448/bin/irb:12:in `<main>'

The main constraint is that the code word shell be evaluated from anywhere, from within a class, module or instance. So it shall be universal.

Solution

  • To gain access to the "main" object from anywhere, use the TOPLEVEL_BINDING:

    class MyShell
  def main_object
    TOPLEVEL_BINDING.eval('self') #=> "main"
  end
end