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describe StatelessCalculator do
  it 'should add some numbers' do
    expect(StatelessCalculator.add(10, StatelessCalculator.add(5, 3))).to eq(18)
  end
 
  it 'should divide some numbers' do
    expect(StatelessCalculator.div(10, 2)).to eq(5)
  end
end

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def add_range_unsafe
  c = StatefulCalculator.new

  threads = (1..256).each_slice(16).map do |range|
    Thread.new do
      range.each { |n| c.add n }
    end
  end

  threads.map(&:join)

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def add_range_safe
  threads = (1..256).each_slice(16).map do |range|
    Thread.new do
      Thread.current[:sum] = range.inject(0) do |memo, n|
        StatelessCalculator.add memo, n
      end
    end
  end

  result = threads.map { |t| t.join[:sum] } .reduce(:+)

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# app/services/calculation_service.rb
class CalculationService
  def initialize(repository)
    @repository = repository
  end
 
  def calculate(operation, x, y)
    result = StatelessCalculator.send operation, x, y
    @repository.save_calculation operation, x, y, result
    result

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class NumberCruncher
  def initialize(calculator)
    @calculator = calculator
  end

  def crunch(array_of_numbers)
    @reduction ||= array_of_numbers.each do |number|
      @calculator.add number
    end

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# app/controllers/calculation.rb
def create
  req = ActiveSupport::JSON.decode(request.body)
  
  calculator = StatefulCalculator.new
  
  # to_crunch => [[1, 2, 3], [9, 10, 11]]
  
  @sums = req["to_crunch"].map do |nums|
    NumberCruncher.new(calculator).crunch(nums)

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# Account = Struct.new(:id, :last_active)

describe 'pruning expired accounts' do
  let(:acc1) { Account.new(1, Date.today) }
  let(:acc2) { Account.new(2, Date.today) }
  let(:acc3) { Account.new(3, Date.today) }
  
  describe 'when the first account is expired' do
    let(:acc1) { Account.new(1, Date.today - 45) }
    

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# Account = Struct.new(:id, :last_active)

describe 'pruning expired accounts' do
  let(:f) {
    # an account factory
    lambda do |id, last_active=Date.today|
      Account.new(id, last_active)
    end
  }
  

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class S3FilePruner < JobProcessor
  def process_job
    Images.all.select do |image|
      image.created_at < Date.today - 30
    end.each do |image|
      S3Object.delete image.s3_object_name, image.s3_bucket_name
      image.destroy
    end
  end
end

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# app/util/prunable.rb
class Prunable
  def self.from_assets(assets)
    assets.select &method(:is_prunable?)
  end

  def self.is_prunable?(asset)
    asset.created_at < Date.today - 30
  end
end