drop_right_while_benchmark.rb

require 'benchmark/ips'

DATA_POINTS = (1..10000).map { |i|
  if i > 8000 # 20%
    { value: nil }
  else
    { value: 1 }
  end
}

module ArrayExtensions
  refine Array do
    def drop_right_while_slow
      self.reverse.drop_while { |el| yield(el) }.reverse
    end

    def drop_right_while_fast
      elements_to_drop = 0
      for index in (length - 1).downto(0)
        if yield(self[index])
          elements_to_drop += 1
        else
          break
        end
      end
      last_index = length - elements_to_drop - 1

      self[0..last_index]
    end
  end
end


class MyClass
  using ArrayExtensions

  def slow
    DATA_POINTS.drop_right_while_slow { |el| el[:value].nil? }
  end

  def fast
    DATA_POINTS.drop_right_while_fast { |el| el[:value].nil? }
  end
end

test = MyClass.new

Benchmark.ips do |x|
  x.report('drop_right_while_slow') { test.slow }
  x.report('drop_right_while_fast') { test.fast }

  x.compare!
end


# =>
# Calculating -------------------------------------
# drop_right_while_slow  355.000  i/100ms
# drop_right_while_fast  352.000  i/100ms
# -------------------------------------------------
# drop_right_while_slow  3.721k (± 4.4%) i/s -     18.815k
# drop_right_while_fast  3.526k (± 2.4%) i/s -     17.952k

# Comparison:
# drop_right_while_slow:     3720.9 i/s
# drop_right_while_fast:     3526.4 i/s - 1.06x slower