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def users_with_discounts
  User.includes(payment_plan: :discounts).where(paying: true).to_a
end

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def users_with_discounts
  @users_with_discounts ||= User.includes(payment_plan: :discounts).where(paying: true).to_a
end

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def users_with_discounts
  return @users_with_discounts unless @users_with_discounts.nil?
  
  users = User.includes(payment_plan: :discounts).where(paying: true).to_a
  @users_with_discounts = users.select do |users|
    users.payment_plan.discounts.any? && !users.payment_plan.delayed?
  end
end

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def users_with_discounts(scoped_to={})
  @users_with_discounts ||= {}
  return @users_with_discounts[scoped_to] if @users_with_discounts.has_key?(scoped_to)

  users = User.includes(payment_plan: :discounts).where(
    paying: true, 
    **scoped_to
  ).to_a
  
  @users_with_discounts[scoped_to] = users.select do |users|

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def users_with_discounts
  @users_with_discounts ||= computation_that_returns_nil
end

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def users_with_discounts
  return @users_with_discounts unless @users_with_discounts.nil?
  @users_with_discounts = computation_that_returns_nil || false
end

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memoized
def users_with_discounts(scoped_to={})
  users = User.includes(payment_plan: :discounts).where(paying: true, **scoped_to).to_a
  users.select do |users|
    users.payment_plan.discounts.any? && !users.payment_plan.delayed?
  end
end

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module RubyMemoized
  class Memoizer
    attr_reader :context, :method

    def initialize(context, method)
      @context = context
      @method = method
    end

    def call(*args, &block)

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class FibonacciCalculator
  include RubyMemoized

  def calculate(n)
    return n if (0..1).include?(n)
    calculate(n - 1) + calculate(n - 2)
  end

  memoized

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require 'benchmark'

Benchmark.bm do |measurer|
  calculator = FibonacciCalculator.new

  measurer.report 'with memoization' do
    10.times { calculator.memoized_calculate(35) }
  end

  measurer.report 'without memoization' do