Calling privilidged methods from sandbox ($SAFE = 4)

test.rb

#!/usr/bin/env ruby

class Sandbox

  @@call = -> this, method, *args do
    this.method(method).call(*args)
  end

  def self.method_added name
    super
    return if name == :initialize || @adding
    @adding = true
    alias_method (name.to_s + '_orig'), name
    remove_method name
    define_method(name, ->(*args) do
      @@call[self, name.to_s + '_orig', *args]
    end)
    @adding = false
  end

  def initialize
    Thread.abort_on_exception = true
    Thread.new do
      $SAFE = 4

      eval "test"

    end.join
  rescue StandardError, SecurityError
    puts $!
  end

  def test
    puts "hello"
  end

end

Sandbox.new