proc

class_a.rb

Class A
  def do_stuff
    b = ClassB.new(word: 'hello')
    
    # does not work
    needs_block_argument(&b.return_the_block)
    
    # does not work either
    needs_another_block_argument(&b.return_another_block)
    
    #does work
    needs_block_argument(&b.return_the_working_block)
  end
end

class_b.rb

Class B
  attr_accessor :word

  def initialize(word:)
     @word = word
  end

  def return_the_block
    -> { "how can i do stuff with #{@word} here?" }
  end

  def return_another_block
    -> { "I can't do stuff with #{word_binding.eval('w')} here." }
  end

  def return_the_working_block
    w = @word
    -> { "now can i do stuff with #{w}" }
  end

  def word_binding
    w = @word
    binding
  end
end