Ruby parallel assignment

Question

I recently wrote the following code:

def freq_progress
 user_flashcards = input_flashcards.includes(:term)
 terms_unicos = user_flashcards.map(&:term).compact.uniq
 freq_1, freq_2, freq_3, freq_4, freq_5 = 0, 0, 0, 0, 0
 terms_unicos.each do |term|
 case term.ranking
 when nil
 next
 when 1..100
 freq_1 += 1
 when 101..300
 freq_2 += 1
 when 301..1000
 freq_3 += 1
 when 1001..2000
 freq_4 += 1
 when 2001..5000
 freq_5 += 1
 else
 next
 end
 end
 {
 f1: freq_1,
 f2: freq_2,
 f3: freq_3,
 f4: freq_4,
 f5: freq_5
 }
 end

In the code review, our technical manager told me that parallel assignment is considered bad practice.

In the Ruby style guide, it says:

Avoid the use of parallel assignment for defining variables. Parallel assignment is allowed when it is the return of a method call, used with the splat operator, or when used to swap variable assignment. Parallel assignment is less readable than separate assignment.

However, I figure that this would apply mostly to situations where each variable is set to a different value, and that my particular use case (setting all values to 0, the same "boring" value) would potentially be an exception to the readability rule.

In other words, it seems that this would emphasize the "equal" nature of the 5 variables.

This may be a matter of opinion, but since the Ruby style guide recommends against it, I’d love to hear what Rubyists more experienced than I have to say about this.

As well as any opportunities for refactoring!

Thanks, Michael

p.s. this question was originally posted on StackOverflow, but I was told to close the question and move it to Code Review.

• greybeard: (One of not too many cases where such a "migration" suggestion seems helpful: Questions bound to get opinions are explicitly deprecated on SO and on-topic at CR.)

Answer 1

Yes, it is generally considered a bad practice because it is considered confusing. Though as you point out it is fairly unlikely to confuse because everything is being set to zeros and the alternative is five lines of repeated code.

However I find myself asking why you don't use an array. i.e.

freqs = [0, 0, 0, 0, 0] or freqs = Array.new(5, 0)

or else just define define the final hash:

def freq_progress
 user_flashcards = input_flashcards.includes(:term)
 terms_unicos = user_flashcards.map(&:term).compact.uniq
 result = { f1: 0, f2: 0, f3: 0, f4: 0, f5: 0}
 terms_unicos.each do |term|
 case term.ranking
 when 1..100
 result[:f1] += 1
 when 101..300
 result[:f2]+= 1
 when 301..1000
 result[:f3] += 1
 when 1001..2000
 result[:f4] += 1
 when 2001..5000
 result[:f5] += 1
 end
 end
 result
 end

• michaelsking1993: Good point on the hash. On the normal SO, somebody commented about the array solution as well. How would this be returned to the frontend? Simply as a 5-positioned array?
• michaelsking1993: Understood - the hash is "required" just because that's how the React client receives it in json. Otherwise, an array would be great. Thanks again.