That's really interesting. Although my worry is the freezing having bad effects down the line after the function returns.

  a = [1, 2]
  
  def check_this(arr)
    raise "doesn't start with 1" unless a.first == 1
  end

  check_this(a)
  
  a << 3 # Raises "FrozenError (can't modify frozen Array)" because check_this froze `a`

Now, if you could temporarily freeze, and then unfreeze only the ones you froze, that could be really cool.