NoMethodError: undefined method `+@' for "some sting":String

Question

My rails app just started receiving this error today. Here is the code context. It is throwing the error on the line that starts with new_host_id

while @host_ids.include?(new_host_id)
  i++
  new_host_id = duplicate_host_id + i.to_s
end

Answer 1

Ruby does not have a ++ operator.

The idiom in Ruby is i += 1, which is the abbreviated form of i = i + 1.

---

Initially I thought that the posted code was incorrect and had to be ++i to generate that error. However, as Jörg W Mittag explains in a comment, this is not the case:

[..] Ruby allows whitespace (including line breaks) between an operator and the operand(s), so the entire thing is interpreted as i + (+(new_host_id = duplicate_host_id + i.to_s)) [.. which is] why the NoMethodError refers to String.

Here is a simplified example showing the issue (the posted code refers to the first case):

> x = "hello"
> +x
undefined method `+@' for "hello":String (NoMethodError)
> x+
syntax error, unexpected $end

I used + and not ++ above to simplify the example: Ruby treats ++i and i++ as the productions +(+i) and [roughly] i+(+) ..