Setting multiple attributes of a Ruby object in a loop

Question

I have a class with bunch of attributes (first, second, third, etc.). I need to go through all "even" attributes (i.e. second, fourth, sixth, etc.) and make some corrections to just those:

report.first = Calculate('1')

report.second = Calculate('2')
report.second *= 0.9 if requireCorrection && report.second > 5

report.third = Calculate('3')

report.fourth = Calculate('4')
report.fourth *= 0.9 if requireCorrection && report.fourth > 5

report.fifth = Calculate('5')

report.sixth = Calculate('6')
report.sixth *= 0.9 if requireCorrection && report.sixth > 5

# etc.

As you can see, I have the exact same code for each "even" attribute, except for the different attribute name. Is there a way to avoid this repetition in the code (I have around 50 attributes in total)?

More importantly, what is your real goal? You might not need such a construct at all. — Eric Duminil
– Eric Duminil, Commented Jul 8, 2017 at 11:45
What does this have to do with pass-by-reference? I notice that you accepted an answer which has nothing to do with pass-by-reference. — Jörg W Mittag
– Jörg W Mittag, Commented Jul 9, 2017 at 9:43
@JörgWMittag typical Ruby behaviour does not allow to pass object to function, but solution were provided - solve this task. — S.ork
– S.ork, Commented Jul 9, 2017 at 14:00
"typical Ruby behaviour does not allow to pass object to function" – What do you mean? That's pretty much the only thing you can do in Ruby. — Jörg W Mittag
– Jörg W Mittag, Commented Jul 9, 2017 at 16:54

Mate Solymosi · Accepted Answer · 2017-07-08 10:13:09Z

1

You can use Object#send to invoke an arbitrary method on report by specifying the method name as a string or a symbol:

def make_correction(report, which_method)
  current_value = report.send(which_method)
  current_value *= 0.9 if current_value > 5
  report.send "#{which_method}=", current_value
end

The method names first, second, third, etc. do not easily lend themselves to automatization, but if you renamed the methods to item_1, item_2, etc., you could use a loop to process all of them:

(1..50).each do |i|
  report.send "item_#{i}=", Calculate(i.to_s)

  if i.even?
    make_correction(report, "item_#{i}") if require_correction
  end
end

If the method names need to stay the same, you can still simplify the code like this:

attrs = [:first, :second, :third, :fourth, :fifth]

attrs.each_with_index do |attr, ix|
  i = ix + 1  # indexes are zero based, we need to adjust them

  report.send "#{attr}=", Calculate(i.to_s)

  if i.even?
    make_correction(report, attr) if require_correction
  end
end

answered Jul 8, 2017 at 10:13

Mate Solymosi

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1 Comment

S.ork Over a year ago

Thanks, that exactly that I searched for!

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