gistfile1.rb

class A
  def initialize(a, &block)
    a.instance_variables.each do |var|
      instance_variable_set(var, a.instance_variable_get(var))
    end
    instance_eval(&block)
  end

  def aaa
    p :aaa
  end
end

@a = 0

instance_eval do
  @a = 1
  @b = 2
  @c = 3

  A.new(self) do
    p [@a, @b, @c]
    aaa
  end
end