gistfile1.rb

class A
  def test(&b)
    instance_eval(&b)
  end
end

class B
  def test_a(a)
    a.test { puts self }
  end
  
  def test_b_helper(*args)
    puts self
  end
  
  def test_b(a)
    m = method(:test_b_helper).to_proc
    a.test(&m)
  end
end

a = A.new
b = B.new

b.test_a(a) #<A:0x007ff66b086c68>
b.test_b(a) #<B:0x007fa3e1886bc0>