Lint error "Literal '+' appeared as a condition" when using ternary if

Question

I have some code. It should remove a trailing + from a string if present:

def remove_prefix(number)
  number.start_with? '+' ? number[1..-1] : number
end

But it doesn't work as expected – it just returns false:

remove_prefix('123')  #=> false
remove_prefix('+123') #=> false

Rubocop shows this error:

Lint/LiteralAsCondition: Literal '+' appeared as a condition.

What am I doing wrong?

Yes... And my method return Boolean, but I expected String value. — Sergey Blohin, Jun 17 '18 at 20:27
FYI: [`String#delete_prefix`](http://ruby-doc.org/core-2.5.1/String.html#method-i-delete_prefix) — Stefan, Jun 18 '18 at 07:59

score 3 · Answer 1 · answered Jun 17 '18 at 20:26

3

bad: number.start_with? '+' ? number[1..-1] : number
good: number.start_with?('+') ? number[1..-1] : number

answered Jun 17 '18 at 20:26

Sergey Blohin

3

...because the former is equivalent to `number.start_with?('+' ? number[1..-1] : number)`. Where `+` is a literal in a conditional `?:`. So Rubocop is thinking, you already know it's truthy, so you might as well have written `number[1..-1]` instead `'+' ? number[1..-1] : number`. Obviously, you have the wrong conditional in the first place, due to parenthesis-less syntax. – Amadan Jun 18 '18 at 01:06
@SergeyBlohin you might want to add some explanation as to _why_ the former is "bad" and the latter is "good" (see Amadan's comment). Both, in regard to the Rubocop warning and the expected result. – Stefan Jun 18 '18 at 10:07

1 Answers1