You probably know that even if your method doesn’t accept blocks, you still can pass them.

def hello(hi)
  puts hi
end

hello('hi') { puts "I'm useless" }
#=> hi

What happens to that block? Well, even though you can’t block.call the block being passed, it is still accessible. For the sake of clearer demonstration I use the method_source gem.

# The `Proc#source` method is powered by method_source.

$block = proc { puts "hi!" }

class Hello
  def hello
    binding
  end
end  

bindval = Hello.new.hello(&$block) #=> #<Binding:0x007fa2b2953d58>
bindval.eval("Proc.new").source #=> "$block = proc { puts \"hi!\" }\n"