Ruby: Use the return of the conditional for variable assignment and comparison

Question

I have a method and in order to check whether it is being passed a block, I do the following:

if block_given?
    res = yield(array[i], array[i+1])
  else
    res = array[i] - array[i+1]
  end

However RuboCop is giving me a warning which I don't really understand in the if block_given? line:

Use the return of the conditional for variable assignment and comparison

Is there any other more rubyist way of doing this?

Thanks

Answer 1

What the warning is telling you to do is:

res = if block_given?
        yield(array[i], array[i+1])
      else
        array[i] - array[i+1]
      end

That is, having a single assignment instead of two (or even more).